Water Quality: Role in Hydroponics
Water quality is one of many determining factors of the outcome in a hydroponic garden. Persistent problems in hydroponic systems are often traced back to the water supply. Water is the basic transportation system in a hydroponic garden as it dissolves and transports nutrients to plants and their root systems, so it is imperative to take the water supply quality into consideration. Also keep in mind, water dissolves impurities not just nutrients. These impurities cannot be easily detected visually, and can be harmful to plants. Hydroponic growers commonly make incorrect assumptions about the purity of water, based on the clarity of a sample. Assuming that the crystal clear, odorless water they get from the tap is pure water, and in turn should be safe for their plants. After all, it’s safe for people to drink … so why not your plants, right?? Wrong. Plants tend to be more sensitive to certain water treatments than people. There are often impurities left in “Safe Drinking Water” that are a problem for your plants, especially in a hydroponic system. City water supply specifications for drinking water vary from city to city. City water supplies are generally treated with chemicals to bring them to drinking quality. These drinking water specs apply to making water that is safe for people, but not necessarily safe for plants.
The EPA has a set limit of a maximum 500 ppm allowed in water, for it to still be considered safe for human consumption. Calcium and Magnesium (or the “hardness” of the water) make up for a portion of the dissolved solids in the water, but how much of the ppm is Calcium or Magnesium and how much is other contaminants? There are a countless number of other substances that can be sources for ppm in your water including agricultural and/or urban runoff, industrial waste, sewage, and natural sources such as leaves, silt, plankton, and rocks. Piping and plumbing have also been known to release metals into the water that also add to the ppm. For example, you test your water and the ppm is 500. The water tastes great to you and others and you think it would be fine to water your garden with. Now, you are in an early vegetative stage and want to keep your feed formula at about 700 ppm. The problem is, your water is already at 500ppm so you are only adding 200ppm of good nutrient value, whereas 500ppm (over double) is unknown solids being fed to your plant !! And that’s the problem! You will not be able to accurately control the amounts of nutrients your plants are receiving. Starting with pure water, as close to 0 ppm as you can get, allows you to add every part of the nutrient formula in the precise quantities required during each phase of growth. Being able to accurately control the content and ppm of your plant food will give you the ability to produce incredible results and have abundant harvests every time. Starting with pure water will also help you avoid nutrient deficiencies or lockout problems. If you do not start with pure water, we recommend having your water tested prior to using it in your garden.
There are many sources or types of water: tap water, reverse osmosis (RO), distilled, rainwater, well water, lake/pond, and even stream water. Each water type or source has its own advantage or disadvantage. The type of issues that growers will encounter will generally depend on the source of their water. Bad water quality can lead to numerous problems such as mineral toxicity/deficiency, stunted growth, mineral/salt build-up, bacterial contamination, etc. The good news is that in most cases, water quality issues have simple solutions that do not involve complicated procedures or techniques. Even beginner growers can use a few simple but effective methods to adequately resolve their water quality issues. There are many causes that can affect water quality, common sources and causes include:
1. Well, Pond, Lake, and Stream Water & Pathogenic Contamination
Well, pond, lake, and stream water tend to have bacteria and soil-borne pathogens (i.e. Pythium, Fusarium Wilt, etc.) in them that are harmful to your plants. Anaerobic bacteria and pathogens can cause a variety of diseases to your plants that can be difficult, if not impossible, to cure. Chlorination is probably the most common form of treatment for bacterial and pathogenic contamination, although you will need to allow the chlorine to dissipate before use in your garden (see ‘Chlorination’ below). Hydrogen Peroxide is also effective as a sterilization procedure, but will also need to be dissipated before use. Hydrogen Peroxide in large amounts will damage your plants. In smaller amounts however, approximately 5ml per gallon of water, hydrogen peroxide can actually be beneficial for plants due to the extra dissolved oxygen in the water and nutrient solution. Beneficial, or aerobic, microbes can also help in suppressing the unwanted pathogens as they will feed on them.
2. Rain water
Rain can be a great source for free, clean water depending on how and where it is collected and stored. If not collected or stored in the proper receptacle, rain water can also contain contaminants. Areas with high pollution will produce acid rain as a result of the raindrops collecting and holding onto pollutants on their way down from the clouds. Rainwater collected from a galvanized iron roof or rain gutters can contain high levels of zinc. Water stored in new cement tanks can contain minerals that have leached into it from the cement. We recommend testing your rainwater prior to using it in your garden.
3. Hard Water and Unwanted Minerals
Many sources of water are considered hard water. Water is considered ‘hard’ when it contains substantial amounts of dissolved calcium, magnesium, and/or other elements. While calcium and magnesium are required by plants, water containing too much (referred to as “Total Hardness”) can create serious problems. You can obtain an analysis of your water supply by contacting your municipal water supplier. If you are using well water, many laboratories will provide you with an analysis if you send them a sample. If your water supply contains 200 ppm or more of dissolved solids, we strongly recommend that you obtain a water analysis to determine the content. Excessive calcium is the major determining factor of whether water is hard or not. If an analysis reveals that the Calcium content of your water supply is greater than 70 ppm you should consider using a nutrient specifically designed for hard water (i.e. Hardwater FloraMicro). Nutrients formulated for hard water provide plants with a combination of chelated micronutrients uniquely composed for hard water conditions.
Hard water can also cause physical problems. High levels of iron, calcium, and lime scale among other elements begin to scale up on water pumps, tubing, heating elements, reservoirs, drip emitters, etc. This causes many problems with equipment clogging, ceasing to work, and can even cause pH problems. Hard water can be cleaned using water softeners. Water softeners use an ionizing resin that back flushes through sodium chloride (salt), replacing the calcium and magnesium ions with sodium ions. This process will then add a small amount of sodium to the water, which is toxic to plants, therefore it is recommended to use Potassium Chloride in your softener as opposed to the more commonly used Sodium Chloride. A Reverse Osmosis (RO) system will be able to take out the contaminants without adding anything to the water, however most RO systems designed for home use only produce a gallon or two per hour. For gardening you would generally want to use an RO system that can provide 100-200 gallons per day. Depending on the RO system and proper filter changes, RO systems can provide a water quality close to that of distilled water. Distilled water is pure water and is free of bacteria and pathogens, but is also free of any minerals or trace elements. If you are using distilled water, you will need to add in about 200-300 ppm of calcium and magnesium to compensate for this. This is also required with RO water. Starting with clean, pure water will give your plants a healthy beginning. Quite often, mature plants that are being fed with water from an un-pure source and are encountering problems, experience significant improvements in health, and growth when switched over to pure water.
City and urban water processing centers most often use chlorination to control levels of bacteria and pathogens. If high levels of active chlorine are in the water you use to make your nutrient solution it can cause damage to several crops, especially sensitive fruits and vegetables such as salad greens, strawberries, and others. The good news is chlorine is highly volatile and evaporates quickly when it comes in contact with air. You can accomplish this by placing chlorinated water in an open aerated reservoir and allowing 48 to 72 hours (depending on the concentration of the chlorine) for the chlorine to dissipate before using it to mix up your nutrient solution. When active chlorine levels fall below 1ppm, it is safe to use for your plants. You can use a water softener to remove chlorine from the water, but keep in mind the issues that come along with a water softener (see ‘Hard Water’ above). Also, you will want to make sure that the water actually contains chlorine, and not chloramines. Many city water processing centers have been using chloramines since before the 1950’s, and there was also a federal mandate to convert the largest U.S. cities to chloramines in 2000. You can’t get rid of chloramines with distillation, leaving the water sit, or even with a standard RO system. Chloramines can be removed with special RO units made to filter chloramines (i.e. a 5 stage RO-deionizer system). Chloramines must come in contact with carbon more often and for longer periods of time to be removed. RO units designed for chloramines usually have more than one carbon filter, and allow the water to move through the filters slower than that of a regular RO system.
7. Iron and Iron bacteria
Iron in the form of iron hydroxide is generally present in ground water sources near areas with deposits of iron sand or iron ore. Iron hydroxide is not directly harmful to plants but will cause blockages problems in various components of your system. If not removed iron bacteria will consume a variety of nutrients that are provided for plant growth in watering systems. Iron hydroxide can be removed by aeration and settling, or flocculation with different agents. Iron bacteria can be removed by sterilization of the water or nutrient solution.
8. Water Temperature
The temperature of your nutrient solution should be in the range of 68 to 72 degrees Fahrenheit. Before adding water to your reservoir, it is a good idea to allow it to come to the same temperature as the water in the reservoir. Plants do not like rapid temperature changes, especially in the root zone. Aquarium heaters can be used to warm the nutrient solution in the winter, and look for “chillers” to cool the solution in the summer if high temperature becomes a problem.