Reverse Osmosis - How to Effectively Remove Excess Hardness, Chlorine and Chloramine From Your Water
In the UK, and in many other countries around the world, we are fortunate enough to have relatively clean water that is safe to drink readily on tap. However, the water in our taps usually comes with a couple of issues which are particularly relevant when we use it to water our plants.
Firstly, the reason that our tap water reaches us disease-free through the water mains supply is that either chlorine or chloramine is added by the water authorities during its treatment. Chlorine and chloramines are highly toxic to bacteria and other micro-organisms, including the beneficial microbes which are becoming more and more popular additions to growers' gardens. If a gardener wants to take full advantage of beneficial microbes, then they will need to have as little chlorine and chloramine as possible present in their feed water. Otherwise they might kill off or inhibit those little organisms by accident!
Secondly, the tap water in many areas of the UK is quite hard and often contains more calcium, magnesium and small amounts of other impurities than is ideal to give to our plants. The ideal starting point for feed water starts around E.C. of 0.4 (CF 4). If you test your water with a nutrient strength meter and it reads more than E.C. 0.7 (CF 7) then there is far too much calcium & magnesium, or other impurities, present for it to be ideal for plants.
Some people say that, on occasion, they can smell the chlorine in their tap water. But even if you can't detect a smell of chlorine, then there is still probably enough in it to be toxic to the beneficial microbes in our plants' rhizospheres. It may not kill them all stone dead instantaneously, but it can certainly inhibit their activity, growth and reproduction.
Let it Stand!
Most of the chlorine will evaporate out of water if it is allowed to stand for about 24 hours. This is the minimum precaution that a grower should take, particularly if trying to grow using micro-organisms ( i.e. biologically). However, chloramine presents a different problem.
Chloramine is a chemically bonded chlorine and ammonia compound that's somewhat more stubborn than chlorine as it does not mostly evaporate out of water within 24 hours. The problem is made worse by the fact that even if a water provider uses chlorine (rather than chloramine) to disinfect the mains water, the chlorine can react with any small amounts of ammonia in the water to create chloramine.
Use a Carbon Water Filter
A carbon water filter will remove the chlorine in water quite readily. However, more contact time is needed between the water and the carbon filter for it to be able to remove chloramines. To achieve a greater contact time, the water needs to pass through the carbon filter much more slowly.
The ideal solution for removing chlorine, chloramine and other contaminants from your tap water is to use a reverse osmosis unit (ideally one that has one or two carbon filters attached).
Best Solution of all - Use a Reverse Osmosis Unit
Reverse osmosis filters work by forcing water through something called a semi-permeable membrane. This very fine membrane allows only the smallest molecules and atoms to pass through it while blocking larger ones. Water (H2O) is a relatively small molecule. Under normal conditions, if a semi-permeable membrane separates a salty solution from a non-salty solution then water will flow through it from the non-salty side. This dilutes the salty-side. This process will continue until either all the non-salty water has passed through it, or the salinity on both sides of the membrane become equal.
In a reverse osmosis system, pressure is used to force the slightly salty water through the membrane and becomes non-salty on the collection side. In other words, the water flows in the opposite direction to when pressure is not being used. The membrane removes 95% to 99% of dissolved salts as well as virtually all bacteria, viruses, spores, chlorine, chloramines and other contaminants in the water as it passes from the mains supply side over to the collection side.
This means that a reverse osmosis system makes water about as pure as is practical in a domestic environment.
This sounds ideal for our plants doesn't it? Pure clean starting water means there's no chance of chlorine or chloramine having a detrimental effect on your precious beneficial soil microbes (the microherd). However, using reverse osmosis water has a knock-on effect that, depending on the nutrient being used, may need to be remedied:
Reverse osmosis, as stated before, removes almost everything out of the water. This includes the calcium and magnesium that is usually found naturally in water. Both of these elements are classed as secondary plant nutrients which means that they are required by plants in moderate amounts. They are not required in large amounts like the macro nutrients N, P and K (nitrogen, phosphorous and potassium) but they are needed in much higher quantities than the micro-nutrients such as iron, boron, manganese, zinc, copper, chlorine, molybdenum and nickel.
Adding back Calcium and Magnesium to RO Water
Some nutrient manufacturers specify that their nutrients are designed to be used with reverse osmosis water while others take account of the fact that growers often use tap water and that there may be calcium and magnesium already present in the starting water. For this reason, when using reverse osmosis water, it is usually necessary (depending on the nutrient being used) to add back some calcium and magnesium with one of the many calcium-magnesium supplementation products on the market.
Alternatively, some growers mix some tap water that's been left to stand for 24 hours in with the reverse osmosis water in order to add back in some of the calcium and magnesium that has been removed. While this helps with the lacking calcium and magnesium levels, it does mean that there is a risk of adding chlorine and chloramine (and other impurities) back in at the same time.
Use RO Water in your Humidifier / Fogger
Another good application for reverse osmosis water is using it in humidifiers. In fact, almost all humidifier manufacturers specify that only reverse osmosis water should be used to avoid invalidating the guarantee. Humidifiers are common pieces of equipment in a grow-space. They work by heating water into a steam and then releasing it into the air. When water containing calcium salts (which is usually particularly high in hard water areas) is boiled, the calcium salts precipitate out as limescale. This is a noticeable effect on the inside of kettles. This limescale build-up progressively damages the inside of humidifiers.
An additional problem is that residual calcium and magnesium in the steam ends up attaching itself to all the surfaces in the vicinity, eventually coating them with limescale. This can cause damage to all your grow equipment, particularly your grow light reflector(s). Because of its removal of calcium and magnesium salts from water, reverse osmosis prevents the problem of scale buildup on your precious growing equipment. As a result, we highly recommend only using reverse osmosis water in your humidifier.
