Water filtration removes suspended solids, chemical contaminants, and microorganisms from water to make it suitable for drinking, cooking, and other household uses. The level of filtration required depends on the source water quality and the intended use. Rainwater, [[Well Systems]] water, and surface water all require different treatment approaches. A multi-stage filtration system is recommended for potable water from any non-municipal source.
Sediment filters remove suspended particles including sand, silt, rust, and organic debris. They are the first stage in any filtration system. Sediment filters are rated by micron size: 50-micron filters remove visible particles, 20-micron filters remove fine sand, and 5-micron filters remove fine silt. Pleated polypropylene cartridges are washable and reusable, while spun polypropylene cartridges are disposable. A backwashable sediment filter uses a media bed of sand or crushed glass that is cleaned by reversing the water flow.
Activated carbon filters remove chlorine, volatile organic compounds, pesticides, and compounds that cause taste and odor problems. Carbon block filters provide both mechanical filtration and adsorption. Granular activated carbon filters are less restrictive to water flow but less effective at removing fine particles. Carbon filters are replaced every 6 to 12 months depending on water usage and contaminant load.
Ultraviolet (UV) sterilization uses a 254-nanometer wavelength UV lamp to inactivate bacteria, viruses, and protozoa. UV treatment is effective against Cryptosporidium and Giardia, which are resistant to chlorine. The water must be pre-filtered to remove particles that could shield microorganisms from UV light. Chlorination is an alternative disinfection method that provides residual protection in the distribution system but produces disinfection byproducts.
Reverse osmosis (RO) systems remove dissolved minerals, heavy metals, nitrate, and fluoride. RO forces water through a semipermeable membrane at high pressure, rejecting 95 to 99 percent of dissolved solids. RO systems produce 2 to 5 liters of purified water per liter of wastewater. They are used for point-of-use drinking water treatment rather than whole-house filtration.