RO efficiency is based upon water temperature and water pressure and not water quality. Low pressure high permeate flow (waste water). Lower the temperature higher the permeate flow. Also low pressures and low temperatures produce lower quality of RO water. That is why pressure booster pumps and permeate pumps are produced for those who are worried about performance and cost of water production. Most people who use RO filters are health conscious more than cost conscious and are only worried about a gallon or two of drinking or cooking water per day and do not notice or care about efficiency or in efficiency, just ready availability and a healthy product. RO operating water pressure is best at 75 psi or higher and 50 psi is considered the minimum operating pressure for a RO filter. If you have low pressure use a pressure booster pump. If you have pressure just above 50 psi get a permeate recycling pump. Still with really poor quality water a RO filter will produce good water cheaper than a DIO filter. Commercial establishments run high water pressures therefore produce RO water efficiently and cheaply. However, they are making a profit which shows that you can produce your own RO water cheaply, just under poor initial conditions start up costs are high if you want cheap water. At 75 psi your permeate will be about 1 to 1.5 gallons per one gallon produced with out a permeate pump. Preheating your water through use of coiled tubing to bring water up to room temperature will cut permeate level down even more. I use a booster pump and my RODI water test out at Zero dissolved solids and is cheaper, safer and much more convenient than store bought, but I put about $600 into setting it up, but it includes a 10 gallon pressurised holding tank, a faucet at the sink with RO water and a seperate line which runs to a DIO filter then a 2 gallon pressure tank that exits through tubing running to a ball valve next to a rubber maid trash can for reef make up water. Clean healthy drinking and cooking water on tap, great coffee water on tap and reef water cheaper than store bought. And it all hides under the kitchen sink, except the faucet and the rubber maid trash can. Melonbob, even in Fairbanks, Alaska RODI water is just 50 cents per gallon at Culligan if you bring your own container. Where are you that you pay that much? As far as what to use the waste water for: the chief thing removed by an RO filter is calcium (hence harder waste water) and phosphate. Heavy metals are removed by both the carbon and RO filter. An increase of 20 to 25% calcium will not make a huge difference in a garden but will gradually raise pH of soil, but for laundry it will increase the need for soap quantity. Most chemicals are removed by the carbon, sediment by sediment prefilters, chlorine by carbon filter. Phosphate and So the permeate water will grow bacteria faster than before it ran through filter so should not be stored for drinking water without adding chlorine, as well the RO water is not considered safely storable for drinking water without chlorine addition, however completely sterilizing the water with UV lights is done quite often for the more expensive bottled waters. The payback period of my RODI filter worked out to be however long it takes to use 2400 gallons of RODI water. Thats with a cost an investment of $600 versus a purchase price of 50 cents per gallon commercially. Consider also $150 of my cost was shipping pieces and parts to Alaska.
