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"Photo of Sand filters"ABOUT WATER SYSTEMS Water Without Borders installs water systems that best meet the needs of the community.

BioSand Water Filters are a technological adaptation of the centuries old slow sand filtration process. While implementations exist in many different sizes and varieties, the most common design is intended for use in rural homes where naturally safe or treated water sources are not available.


BioSand Filters remove 95.0 to 99.0% of organic contaminants, including bacteria, viruses, protozoa, worms, and particles. Safe water produced by the filters is free of discoloration, odor, and unpleasant taste, and can be used for drinking, food preparation, personal hygiene, and sanitation. Most common home-based models can produce between 20 and 60 litres of water per hour.


Osmosis (RO) is a filtration method that removes many types of large molecules and ions from solutions by applying
pressure to the solution when it is on one side of a selective membrane. The result is that the solute is retained on
solventis allowed to pass to the other side. To be "selective," this membrane should not allow large molecules or ions
pores(holes), but should allow smaller components of the solution (such as the solvent) to pass freely.


Reverse osmosis is most commonly known for its use in drinking water purification from seawater, removing the salt and
other substances from the water molecules. This is the reverse of the normal osmosis process, in which the solvent
naturally moves from an area of low solute concentration, through a membrane, to an area of high solute concentration.
The movement of a pure solvent to equalize solute concentrations on each side of a membrane generates a pressure
and this is the "osmotic pressure." Applying an external pressure to reverse the natural flow of pure solvent, thus, is
reverse osmosis.


The process is similar to membrane filtration. However, there are key differences between reverse osmosis and filtration.
The predominant removal mechanism in membrane filtration is straining, or size exclusion, so the process can theoretically
achieve perfect exclusion of particles regardless of operational parameters such as influent pressure and concentration.
Reverse osmosis, however involves a diffusive mechanism so that separation efficiency is dependent on solute
concentration, pressure and water flux rate. Read about one of the reverse osmosis water systems we install.


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