Reverse Osmosis (RO) is the process of moving impurities from your water source. These contaminants- manganese, iron, magnesium, calcium and often large amounts of chlorine- , common in well, spring, and municipal water sources, most often react negatively with your nutrient fertilzer. When starting w/ contaminated water, your total desolved solids ( or parts per million), are already high, leaving less room for your nutrients: nutrient manufacturers assume a water source with a ppm reading of 0. Let me break it down. Say you are in week 2 of the vegatative phase and plan on being at about 400 ppm; If your water source is contaminated, your ppms will already be high. Say you take a reading and the contaminated water reads at 200 ppm straight out of the faucet- now the grower only adds 200 ppm of nutrient solution to hit the suggested 400 ppm, rather than adding the suggested 400 ppm of nutrient solution to RO water that reads around 0 ppm (these numbers are only hypothetical, all water sources differ-drastically!).
But as stated, un-treated water does not just affect the calcubility of your nutirent solution, but it affects the physical chacacterisitcs of the water and its ability to deliver the essential elements to your plants. Hard water will result in a build up in your resevoir, but even more alarming, it can often result in nutrient lock up for your plant. Too much of the elements assocaited with hardwater and your plants will quickly exhibit deficiencies.
Also, some common contaminents in un-treated water promote negative microbial growth that results in root rot, while the chlorine kills the bacteria that is actually beneficial. Treated water allows beneficial bacteria to survive, bacteria that the grower may introduce to aid in root growth, health, and the ability to resist disease. This tactic creates a biological system in the roots that directly affects nutrient uptake, thus overall plant health.
Selecting an RO system is the first step towards having control over your water source, and if you ask any experienced gardener, it is quite an advantageous step. While RO systems require an upfront exspense, this quickly pays off and their filters need only be replaced about once a year. Check out our Hydrologic systems, we find them to be the best. They come in two sizes, depending upon your system's requirements, either 100 gallons per day, or 200 gallons per day. They conveniently hook up to a garden hose and come w/ a feed line.
Another item on the market, which can be used by itself or in conjunction w/ an RO system, is Hydrologics Small Boy and Tall Boy sediment removers. Add it to your RO system to increase efficiency and have a longer filter life, or use it independently. This is not an RO system, but does remove 99% of chlorine and about 90% of sediment, a tremendous upgrade from contaminated water.