Drop of Hope BioSand Water Filter project introducing Shona Grow and Go childrens curriculum into schools in Zimbabwe

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Drop of Hope BioSand Filters

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Drop of Hope - Frequently asked Questions

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Frequently Asked Questions about the BioSand Filter

How much water can be filtered per day?

A BioSand Filter made from the OHorizons Wood Mold will filter 11 liters per use, meaning it will filter 11 liters each time a load of water is poured into the filter. It is recommended to fill the filter a maximum of four times a day and a minimum of one. This means filter owner can get anywhere from 11 to 44 liters of water or approximately 3-12 gallons daily. A maximum of four pours per day is recommended to allow long enough pause periods in between each pour.

How much does a BioSand Filter cost?

The cost will change depending on where the filter is being made and the local cost of materials and labor. Typically, costs range from 25 to 65 USD per filter.

How much does one filter weigh?

An installed filter (with filter media) can weigh up to 350 lbs or 160kgs. Once installed, the filters should never be moved. The settling of the sand helps to improve the pathogen removal and the sand could be disrupted by moving the filter. The concrete filter body weighs approximately 150lbs or 70kgs. If the filter must be moved, then the sand and gravel should be taken out, washed, and reinstalled in the filter's new location.

How long does the biolayer take to develop?

After approximately 30 days of use, the biolayer will be fully developed and the filter will be working at its optimal rate of pathogen removal. During the first 30 days of use the filter is still removing approximately 70% or more of pathogens and effectively removing 100% of chlorine-resistant pathogens. During this period, water from the filter can still be consumed, but we recommend that users additionally boil the water or use chlorine to ensure the water is completely safe to drink.

OHorizons recommends this multi-barrier approach even beyond this initial 30-day period. Although the filter is functioning optimally after the first month, a variety of factors could change its effectiveness over time such as improper use by the user or changes in water source contamination levels. Using a multi-barrier approach throughout the life of the filter ensures users are drinking the safest water possible at all times.

Why does the sand not go down into the hose or PVC pipe?

Sand is only the top layer. The bottom two layers of the filter consist of small and large gravel. The small gravel prevents the sand from leaking and the large gravel prevents the small gravel from leaking or clogging the outlet tube.

Who is responsible for maintaining the BioSand Filters?

It is the filter owner's responsibility to maintain the filter. They are typically trained in maintenance before or during filter installation. OHorizons ensures all of our partners have in-depth maintenance and installation training. These partners are available to households to answer questions, make repairs, re-educate, and provide further assistance, as necessary.

How long does a filter last? How often do you replace the sand?

Barring any unique circumstances that would cause a leak in the concrete body, there should not be any reason to replace the filter. If properly maintained and installed, a filter can last a lifetime and the sand will not need replacement. If using particularly turbid or visually dirty water, the filter owner will use the swirl and dump technique to remove the dirt regularly. This method removes a small amount of sand and over time the filter may need to have some additional filtration sand added to the filter.

Does it need a pump, electricity, or some kind of mechanical system to run it?

No, the BioSand Filter works through the power of gravity. Gravity pulls the water down through the sand and out the hose due to a naturally occurring siphon effect. No electricity or pumps are involved. This means it is a great solution for areas that are not connected to an electrical grid.

A DROP OF HOPE