One of the problems with many homes in rural areas is that there is not enough pressure from pressure pumps to run a reverse osmosis filter system. Reverse osmosis filters work by pushing water against a very fine membrane. Only a proportion of the water, usually 1/4 to 1/3 gets through, leaving behind most salts and other contaminants. The rest of the water with the contaminants goes to waste.
RO systems are designed to remove a large proportion of most contaminants from water including salts and chemicals. The result is very clean water. RO works more efficiently with reasonably clean water like rain water tank or spring water.
The picture is of a boosted RO I made up. It is in the lab and produces rinsing water for the lab and also drinking water for the house. Output is about 108 l/d. It uses a 24 gpd membrane. 50 gpd membranes are also commonly used. The prefilter is just a 1 micron sediment cartridge. The second cartridge is a 1 micron carbon block cartridge. This cartridge is designed to reduce tastes, smells and protozoan pathogens. Here are some results for the lab RO system.
| Before filter | After filter | |
| DOC* by UVA 254 nm | 2.1 ppm | 0 |
| Conductivity | 87 microS/cm | 7.4 microS/cm |
* DOC = Dissolved Organic Carbon. DOC is directly proportional to UVA at 254 nm for most waters. Here an estimate of DOC is made based on an approximate relationship derived from published data from a variety of waters.
There are no detectable dissolved organics getting through and the salts level has been significantly reduced. RO membranes can also reduce bacteria in the water but I haven’t tested bacteria reduction yet.
For a range of water filters to suit both town and country applications see Water Doctor water filters.