Water Quality Considerations in Hydroponics

Water quality is an important determinative factor in hydroponics cultivation. Water is the basic ‘carrier’ in hydroponics as it dissolves and transports nutrients for plants. However, water also dissolves a lot of impurities that can be harmful to plants. These impurities cannot be easily detected visually, and it is all too easy to be misled into making wrong assumptions about the purity of water from the clarity of a sample.
Fortunately, solutions to water quality problems, in the majority of cases, are simple and do not involve complicated methods and techniques. Even small growers can use some simple and proven techniques to effectively solve their water quality problems. The types of water quality problems that growers will likely face depends on the water source from which they draw water for their hydroponics garden.
Poor water quality can lead to a number of plant growth problems including stunted growth, mineral toxicity or deficiency symptoms, build up of unwanted elements in plant tissue, bacterial contamination, etc. Though causes of poor water quality are numerous and varied some of the more frequently encountered of these are
1. Chlorination
Chlorination is the most extensively adopted measure to control bacterial contamination of water supplies in cities, towns and other urban centers. In hydroponics cultivation, the use of chlorine by growers to kill pathogens in their water has caused problems in a number of instances. It was found that this happened due high levels of active chlorine in the water used to make nutrient solution. Chlorinated water sources need to be aerated in a ‘holding tank’ for 48-72 hours (depending on the initial concentration), with good ventilation during which time the active chlorine levels fall to below 1ppm, a safe level for the plant’s root systems. Chlorine in nutrient solution water is known to cause damage to several crops especially to sensitive crops such as lettuce, salad greens, strawberries and others.
2. Unwanted minerals
Water being an excellent solvent dissolves a large number of substances including minerals. While some of these are beneficial, others like sodium, for instance, are quite harmful. Plants do not require sodium and sodium chloride if present in water can cause problems even in small quantities. Sodium can be very harmful especially in re-circulating systems. Plants differ widely in their sensitivity to sodium; some plants like tomatoes can tolerate much higher levels of sodium than other plants such as lettuce. Sodium needs to be kept below 80 ppm for healthy growth of most plants, but below 30 ppm for plants such as lettuce.
Magnesium, calcium, potassium, sulfur, nitrates and trace elements such as boron, copper, manganese and zinc may be present in water from various water sources. This can be taken care of in most cases by suitably adjusting the nutrient formulas to factor in the presence of these elements thus preventing accumulation and toxicities in the water supply. The presence of trace elements can be more troublesome and may require demineralization and dilution of the water source with pure water supply when using in nutrient solutions.
3. Microbial or pathogen contamination
Water from sources such as wells, ponds streams etc. often contains organisms that should be removed before the water can be used in nutrient formulations. The most common of these ‘pathogens’ is Pythium, which can attack plants when present in sufficient spore concentration. Growers have successfully used chlorination as a line of defense against these pathogens, but it requires that the chlorinated water be held for a few days to allow to the concentration of chlorine to drop to levels tolerable to plants. Hydrogen Peroxide can also be used to kill pathogens such as Fusarium wilt and Pythium in water and nutrient solutions.
4. Iron and Iron bacteria

Iron in the form of iron hydroxide is usually present in water from ground water sources near areas with deposits of iron sand or iron ores. The iron hydroxide in water, though not directly harmful to plants presents a number of problems due to the blockages it causes in various components of the system. These blockages if not removed, from an ideal medium for growth of iron bacteria, which consume a variety of elements that are provided for plant growth in hydroponics systems. Iron hydroxide removal methods include aeration and settling or flocculation with different agents. Iron bacteria can be removed by sterilization of the water or nutrient solution.

5. Hard water sources

Water is termed ‘hard’ when it contains substantial amounts dissolved calcium bicarbonate and other elements. When in contact with pipes and equipment the calcium bicarbonate changes to insoluble calcium carbonate also known as lime scale. Hard water forms scale in irrigation pipes, heating elements and pumps causing severe blockages. Computerized water conditioner units similar to the ones used in domestic water supplies can be used to eliminate scaling problems in hydroponics systems.

6. Herbicides

Cases of herbicide contamination of ground water sources and even municipal water supplies are not unknown. Herbicide contamination manifests as damage to sensitive crops such as tomatoes. Activated carbon filtration can help reduce damage but care must be taken to replace the carbon often enough to enable it to retain its efficiency.

Summary

Pure, clean water is essential for healthy plant growth and growers can give the best start to their plants by investing some time and effort in ensuring water quality. Water quality problems are often easy to solve provided they are properly identified. The best approach is to be proactive about water quality as assumptions based on water clarity, absence of visible contamination etc. may be quite misleading.

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