When growing plants hydroponically it is important to consider your source of water, as well as water quality. Due to the lack of organic matter and buffering capacity in hydroponic crop production, poor water quality can negatively impact plants in a short period of time Commercial hydroponic operations routinely test their water throughout the year to monitor make-up and any changes in their water quality and will typically employ some type of water treatment or disinfectant to improve the quality of their water. This is typically not feasible for hobby growers, however, water source and quality should still be considered for hobby growers, as simple and affordable options to improve water quality are available. This article will focus on water source and quality, common issues due to poor water quality, and water treatment options.
Depending on your location and availability of water, you may be using either municipal (city) water or well water as your source water. Each water source has its pros and cons and water quality should be considered before growing and supplying water to plants. If a grower is concerned about their water quality, one can send a water sample to an analytical laboratory for the water contents to be analyzed.
Municipal water is unique to each municipality and will likely change throughout the year. Most municipal water is disinfected with chlorine which can decrease disease pressure of waterborne pathogens, however, if chlorine levels are too high, source water can induce chlorine phytotoxicity in plants. Chlorine levels present in water will be unique to each municipality. Chlorine phytotoxicity symptoms are very similar to root disease symptomology and can cause root browning, wilting, and/or chlorosis. Toxic chlorine levels will depend on the type of plant being grown, type of system being used, and type of substrate being used, however, toxicity has been reported in scientific literature as low 0.3 mg Cl L-1 (ppm). See the water treatment section for dechlorination options if chlorine is a concern in your source water
Well water is also unique to its specific location. Well water can be more alkaline, hard (high mineral content), and may increase disease pressure compared to municipal water. While this is not always the case, well water quality can be very high in some locations.
ALKALINITY AND HARDNESS
Optimum Alkalinity: 60-120 ppm
Alkalinity is a measure of water’s capacity to resist acidic changes in pH (buffering capacity), whereas hardness is a measure of carbonate and bicarbonate present in water. It is ideal to have some level of alkalinity or buffer in water being provided to plants, as this prevents large pH swings of nutrient solution. Unless volume of nutrient solution per plant is quite high (i.e. >5 litres per plant), using water with no alkalinity or buffer will cause nutrient solution pH to fluctuate as the plant grows and uptakes nutrients and water.
CHLORINE AND CHLORAMINES
Chlorine (Cl) and chloramines (NH2Cl) may be present in source water and can cause phytotoxicities. Do not confuse chlorine with chloride (Cl-), which is a plant nutrient. Chloramines are formed when chlorine reacts with ammonium (which may be present in source water or used as a nitrogen source for fertilizer). As stated previously, toxic chlorine levels will depend on the type of plant you are growing, type of hydroponic system you are using, and make-up of growing medium or substrate being used. Toxicity has been reported in scientific literature as low 0.3 mg Cl L-1 (ppm).
Chlorine/chloramine phytotoxicity symptomology:
- Chlorosis (yellowing of leaves)
- Root browning
Chlorine levels can be tested using chlorine test strips used in swimming pools or by using a chlorine test kit (see image below). Chlorine test kits are more accurate than test strips, but also more expensive. Free chlorine meters will measure concentration of chlorine in water, while total chlorine meters will measure concentration of chlorine and chloramines.
WATER TREATMENT AND DECHLORINATION
Many hobby growers will not have the budget to justify treating their water, however, some dechlorination and treatments are relatively inexpensive and feasible compared to more sophisticated water treatment.
Relatively inexpensive and feasible water treatment/dechlorination options for home growers:
Tap Water Conditioners: Tap water conditioners eliminate chlorine and chloramine from water. Conditioners should be added to water before fertilizer is added, as chlorine can degrade EDTA and DTPA chelates commonly used for iron in hydroponic fertilizer. Tap water conditioners are often used for aquarium water before providing water to fish. Be sure that the specific water conditioner being used is safe for consumption if you will be consuming crops.
Carbon/Charcoal filter: Removes chlorine, chloramines, and organic compounds. Will NOT remove microorganisms and minerals. • Aeration/Evaporation: Aerating water or letting water rest in a well-ventilated area for 24-48 hours should remove all chlorine. However, this will not remove chloramines, as chloramines are much more stable than chlorine.
More sophisticated options typically employed in commercial hydroponic operations:
- Reverse osmosis (RO): Effective in removing some microorganisms and minerals. Will need to add alkalinity/buffer back to water to avoid pH swings, unless very large volumes of nutrient solution are being used.
- Water Disinfectant: Ultraviolet (UV) radiation lamps, chlorine dioxide systems, and ozone treatment. Do NOT remove chlorine from water.
Some locations and individuals will not have to worry about their water quality, as it can be very high in specific locations. However, many hydroponic growers will encounter issues with their water quality at some point in time. Taking necessary precautions, using proper testing methods, and using the right interventions, will help growers avoid and alleviate issues, thus ensuring high-quality crops.
Written By - Dan Gillespie