Do You Need to Treat Your Irrigation Water?

Irrigation water should be filtered with a screen at a minimum to remove materials like sand, algae, and soil. This prevents irrigation hoses from clogging and ensures undesirable materials are not transferred to plants. If water is being recycled or reclaimed, it should be reconditioned before use to prevent plants from being exposed to chemical residues and pathogens. The  pH may also need to be adjusted to prevent damage to the plant and growth medium. Greenhouse water testing results can guide in selecting an appropriate filtration system. You may also need to troubleshoot your irrigation system if you are having continued problems.

Be sure not to forget to consider the flow rate of irrigation water. You will want to make sure the water pressure does not push the water through before it has been properly filtered. A 100 or 200 mesh screen filter is suitable for filtering debris in most irrigation systems. Pressure gauges may be installed to ensure that the filter is cleaned or changed when the water flow rate between the gauges decreases by 10% or more.

Water purification systems may use reverse osmosis or ionic filters to purify water when soluble salts and contaminants are an issue. Carbon filters and distillation units also provide advanced purification beyond simple screen filtering. These systems are more expensive and may remove too much calcium and magnesium. If this occurs water may become too soft and falls below ideal alkalinity. Products such as Cal-Mag Solution can be added to increase alkalinity.

Alkalinity, not to be confused with alkaline pH, measures levels of dissolved molecules (bicarbonates, carbonates, and hydroxides) suspended in water. Alkalinity indicates the hardness or softness of water. It is measured as parts per million (ppm) of calcium carbonate (CaCO3). Optimal alkalinity is 30-60 ppm CaCO3 for most plants. pH does not indicate alkalinity, they are two separate tests, and water with neutral pH can have high alkalinity. Some amount of alkalinity may provide additional calcium and magnesium nutrition to plants so fertilizer application should be adjusted considering those levels.

A TDS meter can be used for day to day monitoring of dissolved solids in irrigation water. Lab testing in addition to day to day testing of dissolved solids is highly recommended since TDS meters may not differentiate the type of mineral that is dissolved. In municipal water, alkalinity is of special concern.

High pH generally doesn’t harm plants as long as low alkalinity levels. High alkalinity levels interfere with a plant’s ability to take up nutrients, especially calcium and magnesium. Soil in small containers, especially seed germination trays and plugs, are easily affected by pH and alkalinity of water because there is not as much growth medium to buffer the pH and disperse the dissolved minerals.

Hard water salts such as calcium and magnesium and heavy metals can be detrimental to plants and can clog irrigation systems. High levels of soluble salts can injure plant roots. Some can even burn roots and accumulate in plant leaves. Poor water quality is extremely hazardous to plants. It can result in poor growth and interfere with nutrient uptake. In some cases, nutrient-deficient plants suffer despite sufficient fertilization because salts dissolved in the water supply block the absorption of nutrients.

Electrical conductivity (EC) is the ability of a solution to conduct electrical current (the electrical charges come from mineral salt ions). EC increases as the concentration of these salts increases. EC is a measure used to monitor soluble mineral salts and guides fertilizer adjustments.

Common soluble salts are calcium, magnesium, sodium, chloride, sulfate, and bicarbonate. Small quantities of potassium, ammonium, nitrate, and carbonate can also be detected. These salts come from fertilizer residues not absorbed by plants, and from irrigation water.

Root injury, leaf chlorosis, leaf margin burn, and wilting can be signs that soluble salt levels are too high. Laboratory testing can help determine if a particular mineral salt is the cause of problems. Problems can be avoided by making proper adjustments to fertilizers and irrigation waters, treating irrigation water to purify it, and avoiding the overuse of fertilizers.