When we think of hydroponics, we think of growing plants with nutrient rich water rather than with soil. Thus, we naturally want to use the best nutrients so our plants will be able to grow strong and healthy. But often times the water quality we use is overlooked. However the quality of that water can make or break your plants, even with the best of nutrients. Frequently persistent plant problems can be traced to water quality issues.
Water is the first and largest ingredient of your nutrient solution recipe. Think of it like baking a loaf of bread, if you start with the wrong type of flour, you’ll have nothing but problems trying to bake a good loaf of bread. If you start with the wrong ingredients, you’ll always be trying to compensate for it.
Not all water is created equally. Water doesn’t just hydrate the plant, but it’s also the only source of transportation where the roots have to take up nutrients, as well as distribute them throughout the plant. Water isn’t just water, even safe drinking water can contain all kinds of contaminants, even when it looks and smells crystal clear. Plants are more sensitive to water treatments and contaminants than people are. Tap water, reverse osmosis (RO), distilled, rainwater, well water, lake/pond water, as well as stream water all have their advantages and disadvantages.
Tap and Municipal Water Quality Problems
Municipal city water standards for drinking water vary from place to place. But all of them almost always use various chemicals to bring the water up to drinking water standards. However, the drinking water standards are just the minimum standards that are deemed safe for human consumption. That doesn’t make them necessarily good for your hydroponic plants (or soil plants for that matter), these chemicals can sometimes be damaging to your plants. Sodium chloride (table salt) may even be in municipal city water supply. Sodium chloride is toxic to plants (even in small amounts). This can be a major problem because even small amounts can easily build up over time in recirculating hydroponic systems slowly poisoning your plants.
One of the most widely used chemicals in city water is chlorine. Just like in swimming pools, it’s used to kill bacteria, microflora, and microorganisms (any living organism). Your plants roots are living organisms and higher levels can kill your plants roots as well. Fortunately, chlorine will dissipate quite rapidly, and you can usually smell high levels of chlorine. To allow the chlorine to dissipate before use, simply place it in an open holding tank/container and allow 2-3 days for the chlorine to dissipate. You can speed it up by using an aquarium air pump and air stones to continually circulate and aerate the water forcing it to dissipate faster.
Another issue with city water supply is that it often contains herbicides and herbicides can be quite damaging to hydroponic plants. Fortunately, a good carbon, or carbon/ion filtration system should be able to eliminate chlorine, as well as take out most of these type of contaminates.
Dissolved mineral elements that are useful to plants and are also in hydroponic nutrients like Calcium, Magnesium, Potassium, Copper, Sulphur, Boron, Nitrate, Manganese as well as Zinc can all be present in most water sources. But in what amounts (if at all) is the question? Hydroponic nutrient manufactures try to take this into account, but because the amounts (or lack) of mineral elements vary widely from place to place; excess amounts can change the balance of elements in your nutrient solution. You can check with your city water company and get a water quality report to find out what’s in your water supply.
Problems with using Well, Stream, Lake, Pond, and Rainwater
Water from ground sources is likely to contain pathogenic bacteria, as well as soil born microorganisms, fungi, and other pathogens. Once these get a foothold in your hydroponic system, they can be almost impossible to eliminate. Even after changing the nutrient solution and doing a thorough cleaning, the pathogens will remain on the plant’s roots and in the growing media and then reproduce in the new nutrient solution.
Even rainwater can contain any number of microorganisms, bacteria, fungi and other pathogens depending on how it’s collected and stored. Roof tops, rain gutters, rain barrels etc. are “not” sterile environments. They are all susceptible to being contaminated by bird droppings, dead bugs, and/or animals, decaying foliage, windblown fungal spores etc. All of which is food for bacteria, fungi, and pathogens.
Also rainwater collected from galvanized rooftops, and/or rain gutters may contain high levels of zinc as well. And areas with high smog levels are even susceptible to acid rain. Even water stored in new cement storage tanks can leach minerals into the water supply stored in it.
Water from any of these sources should always be treated before using it in your hydroponic systems. Chlorination as a water treatment before use is probably the most common form of treatment; however, you’ll want to let all the chlorine dissipate before you use it. UV light treatment is an effective way to kill all living organisms in your water supply as well, and it doesn’t have any lingering effects. Any ground or rainwater should always be filtered to reduce dissolved mineral content, as well as sediment after initially killing all living organisms with chlorine or UV.
Reverse Osmoses, Water Softener and Distilled Water
Regardless of whether the source is from municipal city water or ground water, water supplies in most areas are high enough in mineral content to be considered hard water. Not only can this make a balanced nutrient solution unbalanced, but it can also cause problems with pH fluctuations as well.
RO (reverse osmoses) water filtration systems are the best at taking out all types of chemicals, dissolved minerals, and sediment. But not everyone has them and they can be expensive. Most home RO systems only put out a couple gallons per hour, although there are units that can provide 100-200, and even up to 700 gallons per day. However, besides price (if you don’t already have a RO system) another downside to RO systems is that they waste water. While some systems say they only waste 1 gallon of water for every gallon you get (50/50), most systems waste 2-3 gallons of water for every gallon you get to use out of it.
Hard water issues can also be solved using typical household water softeners. They do this by flushing water through ionizing resin and salt. While not noticeable to the taste, this process leaves trace elements of salt in the water. This salt is toxic to plants and can build up in your hydroponic systems and growing media over time, slowly poisoning your plants.
Distilled water is as pure as it gets. It lacks any dissolved minerals, sediment or living organisms. However not only is it impractical due to cost, but it also lacks any trace minerals that nutrient manufactures expect to be in the water and have formulated their recipes with that in mind. This can lead to nutrient deficiencies.
Jeff Sanders runs a hydroponics website called HomeHydroSystems.com to help hydroponics enthusiasts learn how to build their own hydroponic systems and grow hydroponic crops.