The quality of the water we give to our plants plays a big role in the overall quality of not only the plant but the quality of the soil or hydroponic system as well. Different sources of water contain different risks, city water often contains chlorine, chloramines and fluoride as well as the residue of a long journey through aging pipes. Well water can contain pesticide runoff, heavy metals, and above normal levels of calcium, iron or other nutrients. These contaminants can have any number of harmful effects, they wreak havoc on soil microbiology, throw off your nutrient balance, and can be toxic to plants and people. I’m not saying unfiltered water won’t work, it does, but it’s important to know what’s in your water and the better the water the better the plant. You can have your water tested if you are on a well, or find your local water quality report if your on city water. Testing using a standard ppm/tds/EC meter is not an effective measure of water quality as it will only tell you how much is in your water, not what it is, and it won’t detect things like harmful chloramines.
The most common, effective and complete method of filtration available to most growers is called Reverse Osmosis, or RO water, which is what this post is about. RO is the process of forcing a solution through a thin semipermeable membrane that will only let molecules of a certain size through, blocking out anything larger and filtering the solution. This is a very effective method of filtration and can drop your ppm to less than 10 as well as filtering out any chemical contaminants.
There are some downsides to this process though. RO is a pressure based system, using a thin membrane, not all of the water passing through the system is filtered, a portion of it is returned as ‘waste water’. The ratio of filtered water to waste water depends on the size and strength of the RO filtration system, household systems can return as little as 15% of the input water as usable filtered water, whereas a powerful industrial system can return as much as 90%.
Reverse osmosis filtration also serves to keep an even playing field when dealing with nutrients. Here at General Hydroponics, we use RO water in the manufacture of all our nutrients, a key component in maintaining the high level of consistency we are known for. We also base all of our feed charts off of an assumed zero ppm starting point, which is pretty much only achieved using RO filtration. So if you are using RO water, you are starting from the same place we do when mixing your nutrient formula.
Here are couple of personal tips and tricks and frequently asked questions about using RO filters.
I am often asked if a calcium and magnesium supplement, such as CaliMagic, is necessary when using an RO filter. The answer is that it really depends on your specific plants needs. When you use an RO filter, you are filtering out some amount of useful minerals, most often calcium and magnesium. Most base nutrients account for this, as I mentioned before, here at General Hydroponics we base our nutrients off the assumption of zero ppm, so there is plenty of calcium and magnesium in the formula without a supplement. However, many growers have been using unfiltered water on their plants for years, giving them an increased amount of calcium and magnesium, over the years these plants may become accustomed to a higher level of calcium or magnesium and require a supplement, it’s really up to the grower to find out what their specific plants need.
Another method of returning some of the minerals into your filtered water is to mix a portion of unfiltered water back in with your filtered water, if you do this be sure you know what’s in your water so you are aware of what you are putting back in.
A personal tip I have learned to help deal with the large amount of waste water generated by a smaller RO filter is to re-filter the waste water. When you filter your water, you get a percentage of clean filtered water, and an often larger percentage of waste water that contains all the contaminants filtered out of the clean water. This doesn’t mean that this is bad or useless water, it just contains higher levels of contaminants. To conserve water, you can run this waste water back through your filter multiple times. You do run the risk of less successful filtration as the waste water will contain higher and higher levels of contaminants, and it may reduce the useful life of your filter, but it will create substantially less waste water.
Below you can check out Gen Hydro’s RO setup:

Gen Hydro's RO Setup