A water system utilizing a reverse osmotic filter is designed to provide a safe drinking water supply. Municipal water supplies can contain a number of chemicals and microbes which are either not removed by standard processing techniques or are added as part of the decontamination process. Some of these can adversely affect the taste of the water, and certain medical conditions, such as multiple chemical sensitivity (MCS), can be exacerbated by many of these chemicals. Where a drinking water supply is contaminated by microbes, severe gastrointestinal illnesses may result. If a municipal supply is not available, a reverse osmotic system can be used to purify a brackish or saline water supply.
In a reverse osmosis water system, water is forced through a semi-permeable membrane which prevents most of the contaminants and all microbes (including viruses) from passing through. Some chemicals, such as volatile organic chemicals, are not retarded by the membrane; because of this, reverse osmosis systems are often supplemented by a ceramic carbon filter.
The size and type of system to be fitted will depend on expected usage and dwelling size. A small reverse osmosis drinking water system may be fitted in a kitchen to provide a single point of use while the rest of the house continues to be supplied by the water company. On the other hand, a whole house reverse osmotic system will provide safe water throughout a dwelling, but will incur a greater expense. However, a whole house system would still be cheaper than multiple single-use systems. In both cases, the systems will need to be plumbed in.
Water has to be forced through a reverse osmosis water filter, and in areas with low water pressure, a water pressurization system may be required. This adds to both the start up and running costs of the system. Another start-up cost (in addition to the system purchase) is the plumbing work, and ongoing costs include replacement membranes. It is possible to have the membranes cleaned commercially, which will reduce some of the ongoing costs.