Water Quality Checklist for Greenhouse Growers

A quick check of the quality of water you use for irrigation and pesticide application can save you time and headaches in the future.
Water Quality Checklist for Greenhouse Growers - Articles


How good is your greenhouse water?

A quick check now of the quality of water you use for irrigation and pesticide application can save you time and headaches in the future. Using water that is balanced in pH and alkalinity, and is low in suspended solids and dissolved minerals, will improved the growth and quality of your plants and maximize the efficacy of pesticides you apply.

Because the quality of water used in greenhouse production is so critical for proper plant growth and pesticide efficacy, growers should test their water several times throughout the growing season. Here is a quick checklist for busy growers to follow to ensure that irrigation and sprayer water is of adequate quality for rapid and healthy plant growth.

  1. Test. Have a water sample tested at a laboratory that is equipped to test water for irrigation purposes. Penn State provides this service (visit your local Extension office for a water testing kit) as do a variety of commercial labs. A proper water test will include pH, alkalinity, soluble salts (including Ca+ and Mg+, the ions that make water "hard"). Extra tests that may be useful include heavy metals and nutrients.
  2. Filter. Cloudy water is caused by suspended solids. These must be removed from irrigation and spray water. Not only do suspended solids clog up pipes, valves and nozzles, but the suspended material in the water may bind with pesticides in the spray tank, making them less effective in controlling target pests. Simple filters are easy to find and install, but don't forget to clean and maintain them. Pressure gauges installed on both sides of the filter can indicate when it is starting to clog.
  3. Adjust pH and alkalinity. Water for irrigation should fall in the range of 5 to 7 on the pH scale. Acid is used to adjust the pH of water to this range. How much acid is needed is determined by the alkalinity of the water. An alkalinity test measures the level of bicarbonates, carbonates, and hydroxides in water. These anions neutralize acids, so the higher the alkalinity, the more acid must be added to lower the pH. Irrigation water tests should always include both pH and alkalinity.
  4. Check soluble salt levels. If the water test indicates high levels of soluble salts, as measured by electrical conductivity (EC), it may need to be purified or diluted with lower EC water. In some cases, excess sodium (Na+) and chloride (Cl-) in water can harm ornamental plants. Plants may tolerate hard water, i.e. water with relatively high calcium and magnesium, reasonably well, but these minerals can bind with some pesticides, lowering their efficacy. In some cases, water that is high in iron or manganese can cause foliage staining and nozzle plugging. This can be corrected by using a holding tank to allow iron and manganese to settle out, or by the addition of chelating compounds.
  5. Use the correct injector, and make sure it is working properly. If you are using an injector to add acid to your water, make sure it is the right model and is working properly. Regular monitoring and maintenance of injectors is critical.

For an in-depth discussion of greenhouse water quality from University of Massachusetts, check out Water Quality Crop Production.