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. 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.
Then, clean water is essential for healthy plant growth. 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.
Water quality parameters
Different contaminants can interfere with plant developments in hydroponics culture:
Chlorine and chloramines Chlorine and chloramines in nutrient solution water are known to cause damage to several crops especially to sensitive crops such as lettuce, salad greens, strawberries and others. Activated Carbon, placed up-stream of a reverse osmosis membrane is known to remove efficiently those oxidizing agents.
Bacteria and pathogens 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. Moreover, bacteria release ions and organics, which can be harmful for the plant growth. Reducing the level of bacteria and other microorganisms is recommended.
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.
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.
In order to ensure that no minerals like sodium, calcium, magnesium…are present in the high purity water selected for nutrients preparation, water with reduced concentration of these ions is recommended. Decreasing the overall ionic concentration of tap water using reverse osmosis (eliminate > 90 % ions) ensures suitable ionic concentration.
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 deposits it causes in various components of the irrigation system. These deposits form an ideal medium for growth of iron bacteria, which consume a variety of elements that are provided for plant growth in hydroponics systems.
Hardness Hard water forms scale in irrigation pipes, heating elements and pumps causing severe blockages. Use of anti-scaling agents like those used up-stream of a reverse osmosis purification unit reduces hardness prior to reverse osmosis.
Organics (Herbicides) Herbicide residues present in tap and well waters cause important damages 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.
Relatively low TOC value is recommended to ensure good water quality in terms of organic content. Reverse Osmosis specifications totally match with such a recommendation.
Stable water quality is required for hydroponics to operate properly. This can be achieved using a water purification system including Reverse Osmosis (RO) technology to produce the water needed. The usage of RO permits to minimize the fluctuations of the quality of tap water and to decrease the concentration of several contaminants.