Initiative: Safe Water
Frequently Asked Questions
What is the BioSand Water Filter?
The BioSand Water Filter was developed by Dr. David Manz and is a slow sand water filter is specifically designed for intermittent use. This allows the concrete filters to be built on a scale suitable for use by individual households. Prior to this improvement in design, slow sand filters were typically large-scale centralized community filters, reliant upon a continuous flow of water to ensure effective treatment. This design improvement to slow sand filter technology - a technology used effectively to treat water for more than 150 years has allowed for a much broader spectrum of consumers to access it, at very low costs. Slow sand filters have been proven to almost entirely remove the disease-causing organisms found in water. These organisms- known as pathogens include bacteria, viruses, protozoa, cysts, helminths, and worms. The BioSand Water Filter technological adaptation of slow sand filtration has proven as effective as traditional slow sand filters, in both laboratory and field tests. The technology has been introduced in more than 30 countries, by a diversity of organizations and people employing a diversity of means.
How does it work?
As with all slow sand filters, the removal of pathogens occurs in the BioSand Water Filter due to a combination of biological and mechanical processes. Organic material is trapped at, or very close to, the surface of the sand, forming a biological layer. Over a period of one to three weeks, micro-organisms colonize this part of the filter, where organic food and oxygen derived from the water abounds. These micro-organisms consume bacteria and other pathogens found in the water, thereby providing highly effective water treatment. In addition to this process, pathogens are removed as food scarcity and less than optimal temperatures cause their death and subsequent collection at the surface of the sand. Between uses, a layer of water is maintained above the sand at all times.
It is this design feature that distinguishes the BioSand Water Filter from other slow sand filters and which allows for both small scale construction and intermittent use.
What does it look like?
The filter is quite simply a concrete container, enclosing layers of sand and gravel. Water is poured into the top of the filter as needed, where a diffuser plate placed above the sand bed dissipates the initial force of the water. Traveling slowly through the sand bed the water then passes through several layers of gravel and collects in a pipe at the base of the filter. At this point, the water is propelled through plastic piping encased in the concrete exterior and out of the filter, for the user to collect.
What is the difference between the Plastic and Concrete BioSand Water Filter?
Dr. Manz recently granted a license to International Aid to manufacture and distribute a plastic version of the BioSand Water Filter. The concrete filter weigh about 300 pounds and the new plastic filter will weigh less than 10 pounds. The concrete filter has a flow rate of 60 liters per hour while the plastic filter will have a flow rate of 30 liters per hour. The plastic filter will be available through International Aid by January 2007.
How many BioSand Water Filters are in use?
There are several hundred thousand BioSand Water Filters in use in countries all over the world. To get a sense of the use of the technology do a Google search on “BioSand Water Filter”.
Does the BioSand Water Filter remove salt?
No
Does the BioSand Water Filter remove arsenic?
The inventor of the filter has been working in Bangladesh. Dr. Manz has developed protocol for the removal of arsenic that has been accepted by the government of Bangladesh.. MIT has also develop standards that combine the filter and the removal of arsenic.
Are there post filter storage issue to consider?
Yes, it is recommended that a small amount of chlorine be added to the postfiltered water. The chlorine not only eliminates any remaining bacteria but also provides a safeguard against the contamination of the post-filtered water. It is recommended the water is storage in a clean closed neck container to minimize the possibility of contamination during storage.
How many people can use a single filter?
The Plastic BioSand Water Filter will provide about 75 gallons of water per day. The quantity of water is sufficient for the drinking, bathing and cooking need of a family of 5 to 7 people.
What is involved in the maintenance of the filter?
Maintenance is simple. Periodically the flow rate of the filter slows down. Either the bio layer has become very thick or because encrustations build up on the top layer of sand. To restore the flow rate a person needs to remove some of the bio layer and replace with new water and, also, gently stir the top layer of sand with stick or fingers and suspend the encrustation in the biological layer (water). Once this occurs, the water can be scooped out and discarded and replaced with new water. Once the encrustations have been removed the flow rate will return and the filter is back in service. The sand should never need to be replaced.
What type of water can be filtered in the BioSand Water Filter?
Obviously, you want to use the best source available free of solid contamination. Water from a aquaduct, river, lake or water truck is typically used as the water source.
