Hardness reduction is also desirable for efficient operation. These are the typical countertop or undersink systems that rely primarily on the natural water pressure to make the reverse osmosis process function. Undersink units typically utilize a pressurized storage tank where water pressure tends to increase as the tank fills. This provides sufficient pressure to get the processed water to the spigot at the sink. Low pressure units typically provide between 2 and 20 gallons of water per day.
Numbers range from one to ten gallons of waste water per gallon of treated water.
Water purity can be as high as 99 per cent. Depending on efficiency, they can produce water for as little as 10 cents per gallon after maintenance and water costs are factored in. These systems are usually used in industrial and commercial applications where large volumes of treated water are required at a high level of purity. Most commercial and industrial systems use multiple membranes arranged in parallel to provide the required quantity of water. The processed water from the first stage of treatment can then be passed through additional membranes to achieve greater levels of purity.