Household Reverse Osmosis System Components
- Water purification is necessary in today's industrial society.Glass of Water image by Somebody Photo from Fotolia.com
Reverse osmosis water purification systems use ultrafiltration techniques to remove contaminants. These membrane system filters remove particles as small as ions. The membrane has pores approximately 0.0005 microns in size, which removes most bacteria, viruses, organic compounds and salts. It does not filter chemicals such as pesticides, herbicides and chlorine. The entire 5-part system is usually installed under the kitchen sink to treat drinking and cooking water. - Commonly, reverse osmosis systems use pre-filters. One or more pre-filters may be required, depending on the condition of the intake water. Sediment pre-filters are most common and usually made of cellulose acetate. They remove sand, dirt and other sediment. Sometimes, carbon pre-filters are necessary to remove organic contaminants, chlorine and similar chemicals. Both types of pre-filters protect the expensive osmosis membrane from clogging and degradation.
- The reverse osmosis membrane contains tiny pores restrictive to any molecule larger than the pore size. The driving force of a standard residential water system provides sufficient pressure to pass purified water through the membrane. Water with concentrated contaminants is discarded. The membranes remove inorganic chemicals, most microorganisms and most inorganic contaminants. Some systems include an electrical charge which assists in rejection of chemicals from the membrane or an automatic membrane flushing system.
- The ability of the membrane to produce purified water depends on the pressure provided by the water flow. If a flow restrictor was not installed, incoming water would flow past the membrane into the drain line because it is the path of least resistance. The flow restrictor, installed in the reverse osmosis drain line, maintains proper pressure on the membrane, thus allowing the accumulation of purified water.
- Because reverse osmosis works against standard osmotic pressure, the process is very slow. Commonly a residential system provides 15 gallons of purified water per day, recovering only 5 to 15 percent of the total water entering the system. Therefore, a storage tank is required to supply water to the faucet as needed. A standard tank holds about 3 gallons. Inside the tank a bladder keeps the water pressurized to facilitate delivery to the tap.
- After the water leaves the storage tank, before it exits out the faucet, it goes through a post-filter. Post-filters are usually carbon granules or blocks. The post-filter removes undesirable tastes and odors, as well as residual organics. If a carbon pre-filter is used, a post-filter is not needed.
- The reverse osmosis system uses its own delivery tap, installed on the kitchen sink. When the storage tank is full, an automatic shut-off valve conserves water flowing to the drain and a check valve placed after the membrane prevents back-flow from the tank. Preventing back-flow eliminates membrane rupture. Replacement pre-filters, post-filters and membranes are available from many suppliers, but make sure the products are approved by the Food and Drug Administration or the National Safety Foundation.
