Using the BioSand Water Filter for Off-Grid Living

A look into how the BioSand filter, a self-sustaining method of water filtration used in developing regions around the world, can be used in an off-grid setting.

Updated: May 15, 2024
Jeremiah Zac


The most effective water purification system for an off-grid setting is one that requires minimal energy and resources to operate.

Slow sand filtration is one such method that offers a sustainable means of water purification on a large scale.

This article will focus on how small-scale versions of the slow sand filter, such as the BioSand filter, have helped communities meet their clean-water needs without having to rely on outside resources.

What is slow sand filtration (SSF)?

Slow sand filter /

Slow sand filtration is a method of water purification that has been used by societies for centuries, incorporating the use of a biomass layer that eliminates harmful microorganisms in contaminated water.

Early records of slow sand filtration (SSF) systems show that they were used in the 1800s to prevent the spread of waterborne disease outbreaks such as Cholera.

Cholera /

SSF systems became widespread due to their simple resources and design, cost-effectiveness, and ability to serve communities for extended periods of time.

Today, SSF systems of varying sizes are used worldwide and are recognized by the WHO, the UN, and the United States EPA as effective filtration systems for both developing and developed nations. While most modern SSF systems incorporate various technological advances that aid in efficiency, many of the original principles remain the same.

What makes the slow sand filtration process effective?

Of the many possible contaminants present in water, biological contaminants such as Giardia, Norovirus, and various bacteria are the most concerning because the results can lead to extreme illness and death. Some of the most effective methods for purifying water from these biological contaminants require continuous amounts of energy and resources. For example, boiling requires a heat source, and disinfection requires a supply of chemicals such as chlorine.

What makes slow sand filters effective, is that they eliminate biological contaminants without the need for a heat source or chemicals.

The schmutzdecke layer explained

A biomass known as the “Schmutzdecke,” which is German for “dirty layer,” performs the purification mechanism in a slow sand filter.

This layer is formed over the course of about 30 days. Raw water sits on a layer of sand, porous enough to slowly filter through but stagnant enough to allow the biomass to develop. Over time, microorganisms within the raw water begin to multiply, allowing the biomass to develop a more robust company of ravenous hosts. A fully developed biomass will consume any harmful microorganisms present in contaminated water.

BioSand Filter Diagram / CAWST

When contaminated water is added to the slow sand filter, the fully developed biomass consumes the contaminants at the top level. As water is filtered down through the sand, any remaining microorganisms are trapped and eventually die off. The end result is clean water, free of any harmful microorganisms that may potentially cause disease or death.

The main benefit of basic SSF systems is that no additional resources are needed to maintain the purification function. The only initial resources needed are those used to build the system, which mainly includes sand, and structural materials such as concrete, mesh screens, and plastic.

Challenges with traditional slow sand filters

While slow sand filters have certainly revolutionized the way communities can provide clean water to their residents, they’re not without a few drawbacks.

The main issue concerns cleaning and maintenance. As the Schmutzdecke layer builds up, it can often become too thick, impeding water flow, and requiring periodical cleaning of the biolayer to regain optimal water flow for the filter.

For large systems, the cleaning and maintenance of the system can take longer periods of time, disrupting the availability of clean water for communities relying on it. Furthermore, when a biomass layer is in need of replacement, the wait time for another biolayer to grow must commence once again.

These disruptions to the system can often leave some without water for a period of time.

Introducing the BioSand water filter

BioSand Filter Diagram / CAWST

In an effort to address some of these maintenance issues with traditional slow sand filters, Dr. David Manz invented a smaller-scale filter that operates on the same principles but is used and maintained on a per-household basis. With this design, each household is responsible for its own filter but also benefits from it.

He called it the BioSand filter. It was a 1-meter tall concrete filter that could provide up to 36 liters of clean water per hour. It was cheap and simple to build and much easier to maintain than larger, traditional slow sand filters.

BioSand Filter Diagram / CAWST

Dr. Manz designed them as an open-source product to be shared, specifically with impoverished communities.

Because of their convenience and effectiveness, BioSand filters quickly became popular among humanitarian organizations that assist communities in the developing world and those greatly affected by water crises.

Modern uses in humanitarian aid

Today, it is estimated that more than 1.7 million BioSand filters have been implemented in over 60 countries worldwide, benefitting over 8 million people.

Hydraid BioSand Filter / wishingwell foundation

A more lightweight version of the BioSand filter created by NativeEnergy called the Hydraid filter, has also become popular. Replacing the concrete body with a plastic one, the Hydraid filter is more portable, scalable, and affordable than the original design.

How the BioSand water filter can be used in off-grid, self-sufficient living

In self-sufficient, off-grid living, there are no absolutes, only trade-offs. While the idea of having a system that is completely independent of outside resources is attractive, many conveniences will be sacrificed. While it is convenient to run clean water by simply turning on the tap, the system is completely dependent on the local utility service. On the flip side, having your own independent off-grid water source requires a great deal of responsibility to ensure it's purified, acquired, and maintained properly, which is far from convenient.

That’s why the best approach to an effective off-grid water purification system is to find a balance that offers the greatest degree of convenience and independence for your particular conditions, environment, and situation.

A backup for when primary purification methods fail

While the BioSand filter might not be the most convenient or high-output water system, its independence from an energy source or additional chemicals makes it an excellent backup source when other systems fail.

For those who rely on well water and use a whole-house carbon filter as their means of purification, the BioSand filter can act as a backup if the filtration system fails or, in a more extreme situation, if replacement components become inaccessible.

Similarly, for those who rely on rainwater or surface water and use UV light as their primary means of purification, the BioSand filter can act as a backup for when the bulbs or ballasts fail or if and when parts become inaccessible.

Managing the 30-day growth period

Because the biolayer takes time to grow, the wait period can cause a disruption in water accessibility. In order to circumvent this, it is always best to have a backup supply of clean water tucked away in water storage containers. This backup supply can be used while waiting for the biolayer to grow.

Thank you for taking the time to read our article on the BioSand Water Filter. We'd love to hear your feedback in the comments section below. If you've found this article to be useful and are interested in learning more, be sure to sign up for our newsletter.

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I'm Jeremiah, the owner of World Water Reserve. I'm a writer and researcher with a particular interest in sustainability and rural living, water scarcity, and innovative water purification methods. I utilize my multimedia and communication experience in the NGO and humanitarian fields to bring light to important topics. My passion is to educate others on the reality of the global water crisis and on ways to sustain themselves and their families in the midst of it.
Jeremiah Zac