Landscape
And
Nursery
Dialog
Mary Ann Rose
Commercial Landscape
& Nursery Specialist
The Ohio State UniversityJuly, 1998
How to Collect an Irrigation Water Sample
Keywords: irrigation, water testing
What can a water sample tell me? A water sample can provide the alkalinity, pH, soluble salts, and elemental content -- all important considerations for irrigating horticultural plants.
Where to sample? This will depend on what you wish to determine from the sample. If your concern is strictly the quality of water used for irrigating, collect directly from the hose, faucet, or sprinkler head. If you use multiple water sources and are trying to trace the source of a potential problem, sample directly from the various sources, for example, from a well, pond, or stream. If you are concerned about water leaving your nursery, sample both upstream and downstream from your facility (for comparison) or from a drainage tile or other runoff outlet.
When is the best time to collect a sample? When to sample and how often are difficult-to-answer questions. Research is being conducted by Ohio State University on this subject during the 1998 growing season. A number of growers around the state have agreed to submit water samples three times during the season. The combined results should provide some insight into how water quality parameters vary throughout the year.
There are two basic types of water supplies: ground water and surface water. Ground water characteristics tend to be fairly stable unless the well becomes contaminated. Testing every three years should be frequent enough, unless you begin to detect problems.
Surface water includes rivers, ponds, lakes, streams or creeks. These sources generally are more subject to water quality fluctuations than ground water. Temperature, wind, precipitation, biological activity, and runoff from upstream are just a few factors that impact surface water. An annual water test is advisable, although in truth, water quality characteristics may be subject to seasonal, daily, or even hourly changes.
Your specific goals can guide your sample timing. For example, to get a sample that represents the prevailing alkalinity, pH, and nutrient contents, sample under normalā rainfall and irrigation conditions, not during droughts or floods. If potentially high soluble salts in irrigation water are your concern, sample during droughty periods when ponds or wells are low; soluble salts are more likely to be critical at that time. To determine if nitrate levels in runoff are problematic, sample about two weeks after fertilizing, and/or after heavy rainfall or irrigation events.
How do I collect a sample?
- Collect sample in a clean container. Non-breakable plastic is best. Testing labs usually will supply appropriate containers.
- Be sure to supply the amount of water requested by the lab, usually about 1 pint. Failure to do so will result in not getting the results you request.
- If you are sampling from a faucet or irrigation line, allow the water to run for 1-3 minutes to clear the lines of any sediments or deposits.
- Rinse the container with the water source several times before collecting the actual sample.
- Keep your fingers out of the water stream when filling the container This avoids contamination. Filling the bottle all the way to the top will reduce biological activity that may change the water's composition.
- Clearly label and tightly seal the sample container.
- Package the sample well and ship the same day you collect.
Which tests to choose. A commercial or university laboratory can perform the water test. Recommended tests include soluble salts, alkalinity, pH, nitrates, and elemental analysis. At the OSU Research, Extension, Analytical Laboratory, this package costs about thirty dollars. (For further information, call the REAL lab at 330-263-3760). For more frequent tracking of pH and alkalinity, you may purchase test strips or test kits and perform tests yourself. The test strips are marginally accurate . An alkalinity test kit (about $35) is more accurate than strips. Quality, hand-held pH or conductivity meters start at about $250. The pH and conductivity meters are excellent investments for container growers because they may be used to track pH and soluble salts in growing medium as well as test water. Be aware that the sensors do not last forever in these instruments. Ideally, purchase meters with replaceable sensors, and replace sensors every few years. Itās a fact that many, if not most, pH sensors may not last more than a season.
This article was written by Cassandra Sheaffer and Mary Ann Rose. Next month we will cover how to interpret results from your water test.
