Happy 30th Birthday to the Biosand Filter!

We are excited to participate in the 30th year celebration of the biosand water filter! #BSF30

The biosand water filter (BSF) was developed by Dr. David Manz at the University of Calgary, Canada in the 1990s. Committed to providing professional services for humanitarian distribution of the BSF in developing countries, in 2001, Dr. Manz co-founded the Centre for Affordable Water and Sanitation Technology (CAWST). He has trained many organizations on the design, construction, installation, operation and maintenance of the biosand water filter. We are honored to be one of CAWST’s training partners. Pure Water for the World is one of CAWST’s training partners.

Click here to hear Dr. Manz sharing the origin story of the biosand filter.

What is the Biosand Filter?

“This life-saving technology uses sand and gravel to filter drinking water. It’s engineered to be made from local materials anywhere in the world, requires no energy and has no moving parts.” – CAWST

The biosand filter (BSF) is an adaptation of the traditional slow sand filter, which has been used for
community drinking water treatment for >200 years. The BSF is small in size (~3-feet tall, 1-foot wide) and adapted for intermittent use, making it suitable for use in people’s homes.

The BSF container can be made of concrete or plastic. It is filled with layers of specially selected and prepared sand and gravel. The sand layer removes pathogens and suspended solids from contaminated drinking water. A biological community of bacteria and other micro-organisms grows in the top 2cm of sand, called the biolayer. The micro-organisms in the biolayer eat
pathogens in the water, providing water treatment.

How does the biosand filter work?

Contaminated water is slowly poured into the top of the BSF. The water passes through the diffuser and percolates down through the biolayer, sand, and gravel. Treated water naturally flows from the outlet tube.

Pathogens and suspended solids are removed through a combination of biological and physical processes that take place in the biolayer and within the sand layer. These processes include: mechanical trapping, predation, adsorption, and natural death.

How well does the biosand filter work?

Laboratory and field studies of the BSF have proven it removes the following from contaminated water:

  • Up to 100% of helminths (worms)
  • Up to 100% of protozoa
  • Up to 98.5% of bacteria
  • Up to 99% of viruses

The filter can also remove up to 95% of turbidity (dirt and cloudiness) and up to 95% of iron.

Although the water may look clear after filtration, disinfection is still recommended to ensure the best drinking water quality possible. The most common methods used around the world to disinfect drinking water are chlorine disinfection, solar disinfection, and boiling.


As of 2023, CAWST estimates that >1.7 million BSFs have been implemented in 60+ countries around the world, benefitting >8 million people. (source)

Since 2000, PWW has implemented upwards of 20,000 biosand water filters in family homes, schools, orphanages, and health clinics across Haiti and Honduras.

All of PWW’s biosand filter installations include comprehensive WASH (water, sanitation and hygiene) educational training programs that teach about:

  • safe water storage and handling
  • environmental hygiene and water source protection
  • home hygiene
  • personal hygiene
  • menstrual hygiene management

PWW programs incorporate a 3-year, post-implementation monitoring process, to ensure that filters are being used correctly and consistently and communities are experiencing improved health outcomes.

*Preliminary results from a recently conducted 10-year monitoring study is reporting 100% of families are continuing to consistently use PWW-implemented safe water filters 10 years after installation.

“Before PWW came to our community, I didn’t consume clean water because I get my water from a well that is easily contaminated by animals and people. My daughter has dealt with a lot of stomach pain and illnesses, and so have I, because we did not treat the water.

From the day the PWW project arrived, our situation changed. PWW helped us with a toilet and a biosand water filter.

Today I feel blessed and grateful to God and to all of the PWW staff. Thanks to them, today we drink clean filtered water. My daughter does not suffer from stomach issues anymore. Also, now we have a personal toilet, so we no longer will be polluting the environment. I feel happy. Thanks to the donors and PWW.”

– Rosa Maria Ochoa Velásquez, El Coyote, Honduras

We are infinitely grateful to Dr. Manz for taking his inspiration into action. And special thanks to our dear friends and partners at CAWST, who continue to support and advance the work of PWW teams in Honduras and Haiti. We are grateful for CAWST’s unrelenting commitment to expand access to safe water for people across the globe!