Explore Biosand Filter

Follow the series of step by step instructions to build and install a biosand filter (BSF) from start to finish.

This poster set includes water, sanitation and hygiene (WASH) posters to teach about good WASH practices, including household water treatment technologies.

This collection of competency frameworks can be used by individuals and organizations in two main ways: Assess job performance and compare it against defined standards Identify potential areas for professional development to improve overall performance Competencies are the abilities required to perform specific tasks and express specific knowledge. CAWST’s competency frameworks use behavioural or task-based competencies in combination with knowledge components.

This collection contains the resources for both trainers and participants for the Biosand Filter Project Implementation workshop. This workshop is designed for biosand filter project managers and technicians. This workshop includes information and hands-on experience on the construction, use and monitoring of the biosand filter. The hands-on topics include checking the steel mold, making the concrete filter container, preparing filtration sand, installing filters and conducting follow-up visits. The participant will gain a clear understanding of the rationale behind the filter design and why proper preparation of the filtration sand is so important.

This collection contains the resources for both trainers and participants for the Household Water Treatment and Safe Storage Program Design workshop. The intended participants are people responsible for making decisions about HWTS program design and implementation.

Discover how other people run their HWTS projects, what works and what they would change if they could by checking out the following case studies and resources.

This collection contains the resources for both trainers and participants for the Household Water Treatment and Safe Storage workshop. This two to three day workshop provides an introduction to drinking water quality, the Multi-Barrier Approach to safe drinking water, household water treatment and safe storage (HWTS) options, behaviour change, and implementation best practices. The intended participants are people responsible for making decisions about HWTS selection and implementation.

Watch and share these 9 videos to learn more about how a biosand filter works, how to use it and how to maintain it.

This collection contains the resources to support the professional development needs of our clients and partners in biosand filter quality control. It contains an overview of our competency framework, as well as useful tools to help biosand filter technicians improve their skills. The competency framework includes tools for three different areas: constructing concrete boxes, preparing the filtration sand and gravel, and installing filters.

This collection contains the resources for both trainers and participants for the Monitoring for Biosand Filter Projects. This five day workshop is primarily designed for biosand filter technicians, community health promoters and project managers. The workshop provides background on how and why this service was developed, tips to help you plan for a successful consultation, and several tools to help deliver your training, such as monitoring forms, checklists, lesson plans and case studies.

This collection contains the resources for both trainers and participants for the Biosand Filter for Technicians workshop. This three-five day workshop is designed for biosand filter technicians. This workshop includes instruction and hands-on experience in construction of the biosand filter – including the concrete container, filtration sand and gravel, diffuser, and lid. The participant will gain a clear understanding of how to construct a filter, how to install the filter, and how to instruct end users on its correct use and maintenance.

Part of a video series on how to build a biosand filter (BSF). Learn step by step how to disinfect the outlet tube after installation.

This video will teach you how to perform a sand grain size analysis.

An instructional video on how to build a biosand filter

This appendix from the Biosand Filter for Technicians Construction Manual includes monitoring forms.

Watch how a mechanical sand sorter can simplify the sieving and sorting of gravel and sand into correct sizes to build a Biosand Filter (BSF).

Learn how to get the concrete mix just right before pouring the Biosand Filter (BSF). Get tips and tricks to get the right concrete consistency to get a strong filter body with a smooth, even surface.

Part 1 of a series on how to construct a biosand filter (BSF). Learn how to sieve the gravel and sand to the proper size and how to separate the piles to keep the quality consistent.

Part of a video series on how to build a biosand filter (BSF). Find out how to correctly wash the separation and drainage gravel layers used when installing a BSF.

Part of a video series on how to build a biosand filter (BSF). Find out how to correctly wash the filtration sand used when installing a BSF.

Part of a video series on how to build a biosand filter (BSF). It shows step by step how to check the quality of a newly constructed BSF. Learn how to check for flowrate, leaks or cracks and water level. Then how to cure the concrete to make sure the filter will work well for years to come.

Part of a video series on how to build a biosand filter (BSF). Learn how to remove the concrete filter from the steel mold when the concrete mixtures used to pour the filters were too wet or too dry.

Learn step by step how to correctly install a concrete BSF filter with layers of gravel and sand and how to check the flowrate. Learn tips to make filter installation efficient.

See different Biosand Filter (BSF) designs and learn how to install them correctly.

Part of a video series on how to build a biosand filter (BSF). Learn step by step how to remove a concrete biosand filter (BSF) from a steel mold. Learn tips to make demolding the filter easier and to prevent damage or cracks.

Learn what to look for when using a steel mold to build a Biosand filter (BSF). Tips and valuable information about the steel mold will help you successfully construct concrete filter bodies.

Learn how to clean and oil a Biosand Filter (BSF) mold and to install the outlet hose before pouring the concrete container to achieve a smooth, trouble free concrete filter body.

Part of a video series on how to build a biosand filter (BSF). It shows step by step how to pour the concrete into the mold to avoid air pockets and to eliminate cracks between the concrete layers.

Part of a video series on how to build a biosand filter (BSF). It shows the pitfalls of using too wet and too dry concrete mixtures when pouring a BSF concrete filter body.

Part of a video series on how to build a biosand filter (BSF). Learn how to remove the concrete filter from the steel mold when the concrete mixtures used to pour the filters were too wet or too dry. Check the quality and see if the filters meet the standards.

Part of a video series on how to build a biosand filter (BSF). It shows step by step how to check the quality of a newly constructed BSF. Learn how to check for flowrate, leaks or cracks and water level. Then how to cure the concrete to make sure the filter will work well for years to come.

Part of a video series on how to build a biosand filter (BSF). It shows the pitfalls of using too wet and too dry concrete mixtures when pouring a BSF concrete filter body.

Part of a video series on how to build a biosand filter (BSF). Learn step by step how to remove a concrete biosand filter (BSF) from a steel mold. Learn tips to make demolding the filter easier and to prevent damage or cracks.

Part of a video series on how to build a biosand filter (BSF). It shows step by step how to pour the concrete into the mold to avoid air pockets and to eliminate cracks between the concrete layers.

Part of a video series on how to build a biosand filter (BSF). Find out how to correctly wash the separation and drainage gravel layers used for installing the filters.

Part of a video series on how to build a biosand filter (BSF). It outlines how to correctly install a concrete BSF with layers of gravel and sand and how to check the flowrate.

Part of a video series on how to build a biosand filter (BSF). It oulines what to look for in a BSF steel mold. It includes tips and valuable information about the properties of a mold for the successful construction of a BSF concrete filter body.

Part of a video series on how to build a biosand filter (BSF). It outlines how to clean and oil a BSF mold and to install the outlet tube before pouring the concrete container to achieve a smooth, trouble free concrete filter body.

Part of a video series on how to build a biosand filter (BSF). It outlines how to correctly mix the concrete before pouring the BSF body. It includes tips and tricks to get the right concrete consistency to get a strong filter body with a smooth, even surface.

This video interview explores why to use Drinking Water Quality Testing (DWQT) when implementing a Biosand Filter (BSF) project. The interview with experienced BSF implementers includes Lalit Sharma of Sehgal Foundation (India), Elijah Mutafya of Seeds of Hope International Partnership (Zambia) and Suneel Rajavaram of CAWST (Canada) sharing their experiences using DWQT in support of their BSF projects.

Part of a video series on how to build a biosand filter (BSF). It outlines how to install alternative BSF filter designs.

Part of a video series on how to build a biosand filter (BSF). It demonstrates how to sieve and sort gravel and sand using a mechanical sand sorter to ease the work load when preparing construction materials to build a BSF.

Part 1 of a video series on how to build a biosand filter (BSF). It demonstrates how to sieve and sort gravel and sand to maintain consistent quality during construction of a BSF.

The Business Model Canvas is a one page business plan that clearly sets out the nine key elements you need to consider in planning your business. The Business Model Canvas was created in 2010 by Osterwalder and Pigneur. This canvas describes Aqua Clara Kenya's market-based approach to deliver biosand filters and membrane filters, handwashing and safe water storage containers to consumers in Kenya.

The Business Model Canvas is a one page business plan that clearly sets out the nine key elements you need to consider in planning your business. The Business Model Canvas was created in 2010 by Osterwalder and Pigneur. This canvas describes The Safe Water Project's market-based approach to deliver biosand filters and bottle refilling services to consumers in South Sudan, Uganda, and Kenya.

Learn more about this Biosand Filter Project in Colombia.

Learn more about this Biosand Filter Project in Colombia.

This video from an HWTS learning exchange in Colombia, 2019, provides a lot of inspiration and insights from participants as they share their experiences implementing HWTS programs.

This video outlines regulatory changes made by the Government of Colombia to enable Household Water Treatment as a method to acheive more universal access to safe drinking water.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This animated instructional video is one of 9 videos in a series on the operation and maintenance of the biosand filter (BSF). The videos have been designed to educate end users of the filter and as a resource for organizations distributing the filter. The "No Voice" version can be used to dub the videos into a local language. English transcripts are provided. You can download a mobile or desktop app with all of the BSF videos at www.cawst.org/bsfvideos. These videos have been produced by CAWST.

This competency assessment tool was designed by CAWST to measure and guide the professional development of BSF Technicians in the area of installation.

This competency assessment tool was designed by CAWST to measure and guide the professional development of BSF Technicians in the area of box construction.

This competency assessment tool was designed by CAWST to measure and guide the professional development of BSF Technicians in the area of sand.

This fact sheet describes filtration of drinking water using a biosand filter.

In 2011 Samaritan’s purse, in Cambodia, utilized slow sand filtration and BSF principles to develop a filter appropriate for institutional scale use, such as that of schools. In 2012 a standard design was developed and subsequently a performance study was conducted in 2014 affirming the efficacy of the design principles in E.coli removal. Since then, Samaritan’s purse has continued to adapt the standard design in multiple contexts in 8 countries around the world to address biological contamination. In January 2017, Samaritan’s Purse in partnership with CAWST, published “Technical Manual: Intermittently Operated Slow Sand Filtration (iSSF) System” to be used by implementers wanting to use the design. Samaritan’s Purse has surveyed its field staff to provide updated insight on field adaptations of the technology and in this session will reintroduce basic design principles as alignment with the published manual as well as applicable insight gleaned since the January 2016 webinar hosted by CAWST.

This case study describes Aqua Clara Kenya's household water treatment initiatives in Kenya.

In this lesson, participants will look at how to use and maintain a biosand filter. This lesson will also focus on how a Community WASH Promoter can verify that a household is using their filter correctly, consistently, and continually.

This technical manual, written by Samaritan's Purse Canada and CAWST, is a guide for potential implementers of the intermittently operated slow sand filter (iSSF, also called the school biosand filter). This manual outlines principles and best practices for adapting, installing, commissioning and maintaining the filtration system.

The most important part of the biosand filter is the filter sand. It is the sand that does the actual work of removing dangerous pathogens from the water. Biosand filters can come in all shapes and sizes, with filter containers successfully being made from concrete, plastic, PVC, ferrocement, sheet metal, and other materials. However, if the sand is not right, the filter will not work. This webinar goes over the most important aspects about filter sand, reviews the latest research, and addresses common questions and challenges people run into in their projects.

This is a CAWST webinar that covers the most important aspects of biosand filter sand. It includes the latest research and addresses common questions and challenges people run into in their projects.

Good maintenance practices of the biosand filter will ensure good quality water.

The biosand filter can provide good quality water.

A video recording of the webinar on October 21, 2015 - Biosand Filter - Virus removal Q&A. While a recent study showed that virus reduction in biosand filters can meet USEPA and WHO standards, the mechanism(s) influencing virus reduction are still not clear. This webinar will discuss virus reduction (specifically the MS2 virus) as a function of physical filter characteristics (depth, media aging, and residence time) and microbial communities throughout the filter. Further understanding the mechanism of virus reduction in biosand filters is necessary and can help to enhance the design.

This is a CAWST webinar that covered the most important aspects of biosand filter sand. It included the latest research and addressed common questions and challenges people run into in their projects.

A video recording of the online training session on May 2, 2013 - Biosand Filter designs, molds, sand selection and sieve analysis, follow-up monitoring tools and costing.

This questionnaire is to be handed out at the end of the workshop to give the trainer constructive feedback on the workshop

This is a template of how to display the results of your final evaluations

This is a template for the final workshop evaluation

This is a template of how to display the results of your final evaluations

This is a template for summarizing the final workshop evaluations

This document contains all of CAWST's case studies on biosand filter project implementation, in various countries, by various implementers.

This case study describes EDES's implementation of biosand filters in Peru.

This case study describes Agua Pura Para el Mundo's implementation of biosand filters in Honduras.

This case study describes Hecho's 2:8's implementation of biosand filters in Guatemala.

This document describes how to construct a mini sand sieve set. The sieve set is used to do a sand grain size analysis, which helps you select sand from a supplier to use as filtration sand inside biosand filters.

This document summarizes published studies and information about biosand water filters

This presentation describes criteria for choosing appropriate HWTS options (Designed for Lesson Plan 8 of the BSF for PI Trainer Manual)

This manual is for project implementers who are interested in starting a biosand filter project

This presentation identifies the parts of the filter, their function and how the biosand filter works (Designed for Lesson Plan 10 in the BSF for PI Trainer Manual)

This questionnaire is to be handed out at the end of the workshop to give the trainer constructive feedback on the workshop

This questionnaire gives the trainer feedback mid way through the training in order to help the trainer better prepare and create relevant sessions

This costing sheet will help you determine your budget for implementing a biosand filter project

This questionnaire helps the trainer to understand their audience and their level of knowledge pre-workshop

This participant List template is a tool that will help you keep a database of participant information

This presentation describes the F Diagram of disease transmission

This presentation describes how the biolayer develops and how it helps filter water (Designed for Lesson Plan 10 in the BSF for PI Trainer Manual)

This presentation describes common water related diseases

This document describes the technical specifications of the 0.7 mm (24 mesh) screen. This screen is required to make sieves for screening the filtration sand that goes inside the biosand filter. A short list of global suppliers, where known to CAWST, is also included.

This document describes how to convert CAWST Version 9 biosand filter molds to Version 10 molds.

This document lists things to check on a steel biosand filter mold to ensure it has been constructed well and/or maintained well to produce high quality biosand filters that are easy to remove from the mold.

This appendix of the Biosand Filter Construction Manual contains costing tables that can be used to calculate budgets for biosand filter projects

This document contains drawings and instructions for constructing CAWST Version 10 biosand filter molds with no ledge for a diffuser plate. This mold will produce filters that must be used with a diffuser basin that hangs from the top of the filter, as there will be no ledge or lip inside the filter on which to sit a diffuser plate.

This document contains instructions for constructing sand sieves. Several sieves are required to screen sand to the proper sizes for constructing and installing biosand filters.

This document describes the procedure for doing a sand grain size analysis. It contains step-by-step instructions on how to do the analysis, graph the data, and calculate and interpret the results.

This document contains extra graphing and calculation sheets to use for a sand grain size analysis. To be used with the Sand Grain Size Analysis Instructions.

This document contains drawings and instructions for constructing CAWST Version 10 biosand filter molds with a ledge for a diffuser plate. This mold will produce filters that may be used either with a diffuser basin that hangs from the top of the filter (prefered), or a diffuser plate that sits on the ledge or lip inside the filter.

This outline describes the content, objectives and audience for CAWST's workshop: Biosand Filter Project Implementation.

This spreadsheet contains budget tables that can be used to cost out or budget for a biosand filter project. It can also be used to track on-going project costs.

This document can be used as a workbook to plan household water treatment projects.

This spreadsheet describes the procedure for doing a sand grain size analysis. It contains step-by-step instructions on how to do the analysis, enter the data, and interpret the results.

This presentation shows different finished filters (Desgined for Lesson Plan 17 in the BSF for PI Trainer Manual)

This presentation shows three mold models for the biosand filter

This presentation describes local and global water issues and how they perpetuate the poverty cycle (Designed for Lesson Plan 2 in the BSF for PI Trainer Manual)

This presentation describes different types of containers used to make biosand filters

This presentation describes the five steps of the multibarrier approach to water treatment (Designed for Lesson Plan 6 in the BSF for PI Trainer Manual)

This presentation describes what is necessary for behaviour change (Designed for Lesson Plan 29B and 39C in the BSF for PI Trainer Manual)

This presentation describes HWTS options and their pros and cons (Designed for Lesson Plan 6 and 7 in the BSF for PI Trainer Manual)

This document is a series of photos and descriptions of a welder making a steel biosand filter mold. It is intended to be used alongside the mold fabrication instructions, to help a welder and/or project implementer understand how to construct a high quality mold.

This illustrated manual describes what a biosand filter is and how it works. It also describes the steps to construct, install and monitor Version 10 biosand filters.

This appendix from the Biosand Filter Project Implementation Construction Manual includes monitoring forms.

This presentation describes local and global water issues and how they perpetuate the poverty cycle through the lens of the MDGs (Desgined for Lesson Plan 2 of the BSF for PI Trainer Manual)

This presentation shows different types of sand sieves

This presentation shows different lid options for biosand filters (Designed for Lesson Plan 18 in the BSF for PI Trainer Manual)

This presentation describes the three components of implementation (short version) (Designed for Lesson Plan 38 of the BSF for PI Trainer Manual)

This presentation describes the three components of implementation (long version) (Designed for Lesson Plan 38 in the BSF for PI Trainer Manual)

This presentation describes the four ways biosand filters remove pathogens (Designed for Lesson Plan 11 in the BSF for PI Trainer Manual)

This presentation describes the four types of pathogens and the waterborne diseases they cause (Designed for Lesson Plan 4 in the BSF for PI Trainer Manual)

This presentation describes how to transport biosand filters

This presentation shows different diffuser options (Designed for Lesson Plan 18 in the BSF for PI Trainer Manual)

This presentation describes how the biosand filter works while its being used (Designed for Lesson Plan 11 in the BSF for PI Trainer Manual)

This presentation describes the 8 things to check to make sure a biosand filter is working (Desgined for Lesson Plan 12 in the BSF for PI Trainer Manual)

This presentation describes why it is important to safely store treated water and how to store it

This manual is for trainers who are interested in delivering training for biosand filter technicians. It includes lessons plans and guidance on training delivery.

This is an agenda for a BSF building workshop with a focus on troubleshooting problems

This is an agenda for a BSF building workshop with a focus on the building process

This presentation describes the four ways biosand filters remove pathogens (Designed for Lesson Plan 11 in the BSF for Tech Trainer Manual)

This is a template for creating a participant list

This outline describes the content, objectives and audience for CAWST's workshop: Biosand Filter for Technicians

This is an agenda for a 4 day BSF building workshop that includes the theory of clean water and how to do follow up visits

This is a template for writing a workshop report

This is an agenda for a 5 day BSF building workshop that focuses on troubleshooting practice

This is an agenda for a 5 day BSF building workshop that includes more theory on how the BSF works and why water should be filtered

This presentation describes the five steps of the multi-barrier approach to water treatment (Designed for Lesson Plan 6, 7, 8 in the BSF for Techs Trainer Manual)

This presentation describes how the biolayer develops and how it helps filter water (Designed for Lesson Plan 10 in the BSF for Tech Trainer Manual)

This presentation explains the steps of household water treatment and gives criteria for evaluating different options (Designed for Lesson Plan 10 of the BSF for Techs Trainer Manual)

This presentation describes common water-related diseases (Designed for Lesson Plan 5 in the BSF for Techs Trainer Manual)

This presentation shows pictures of finished biosand filters (Designed for Lesson Plan 17 in the BSF for Tech Trainer Manual)

This presentation describes the four types of pathogens and the water-related diseases they cause (Designed for Lesson Plan 4 in the BSF for Techs Trainer Manual)

This presentation describes how the biosand filter works while its being used (Designed for Lesson Plan 11 in the BSF for Techs Trainer Manual)

This presentation describes the 8 things to check to make sure a biosand filter is working (Designed for Lesson Plan 12 in the BSF for Tech Trainer Manual)

This presentation describes how to transport biosand filters

This presentation describes the function of diffusers, what makes a diffuser effective and options for diffusers (Designed for Lesson Plan 18 in the BSF for Tech Trainer Manual)

This presentation identifies the parts of the filter, their function and how the biosand filter works (Designed for Lesson Plan 10 in the BSF for Techs Trainer Manual)

This manual is for biosand filter technicans who are interested in learning how to construct, install and monitor biosand filter projects. This manual has less information about how the biosand filter works, compared to the "Biosand Filter Construction Manual."

This workshop outline contains a workshop description, objectives, audience, content and training materials needed for this workshop

This participant List template is a tool that will help you keep a database of participant information

This questionnaire helps the trainer to understand their audience and their level of knowledge pre-workshop

This questionnaire gives the trainer feedback mid way through the training in order to help the trainer better prepare and create relevant sessions

This agenda lays out how to run a 5 day workshop on BSF project monitoring that includes theory and field practice

This manual is for trainers who are interested in delivering training on how to monitor BSF projects in order to improve their quality. It includes lessons plans and guidance on training delivery.

This is a case study of a biosand monitoring project in Haiti

This is an agenda for a BSF workshop that reviews the importance of clean water, how to build the biosand filter and how to troubleshoot problems

This manual is for project implementers who want to improve and strengthen their biosand filter projects.

This case study describes Aqua Clara International's monitoring program for biosand filters in Kenya.

This large poster of a Version 9 biosand filter (cross-section) can be printed for a training session or community event. *Note: This resources is for projects implementing the older Version 9 filters.

This poster of a Version 9 biosand filter can be used as a puzzle activity in a training session or comminuty education event. *Note: This resources is for projects implementing the older Version 9 filters.

This large poster of a Version 10 biosand filter (cross-section) can be printed for a training session or community event.

This poster of a Version 10 biosand filter can be used in a training session or comminuty education event to show how the sand, small gravel and large gravel are layered inside the filter.

This document shows an example of the graphing and calculation for a sand grain size analysis. To be used with the Sand Grain Size Analysis Instructions.

This documents contains answers to frequently asked questions about biosand filters.

This document from BushProof contains construction guidelines for building a round steel mold for biosand filters.