Pastures Flooded with Potentially Contaminated Water: Is it safe?

Pastures Flooded with Potentially Contaminated Water: Is it safe?

After pastures have been flooded, taking precautions when turning out for grazing is important. Once the pastures dry out and receive adequate sunlight, the bacteria that were on the grass in pasture will be eliminated.  However, the standing water that does not evaporate may be an issue depending on how much rain has occurred to dilute out the flood water. Thus, it is recommended that producers sample standing water in pasture a couple weeks before they want to turn out to see how much potential nitrates and coliform bacteria are present. If there is potential for the water to have been contaminated with chemicals (pesticides for instance) then toxicology screening may also be desirable.  

There are two scenarios: fresh water is available in pastures versus standing water being the sole water source.

If fresh water is provided to livestock in a previously flooded pasture, the concern with grazing pasture is that any standing water available could be consumed. Since the livestock have access to fresh water, the risk of toxicity would be lowered and thus providing fresh water access is recommended. However, testing the standing water to ensure water they could potentially drink would not harm the animal is a good risk management strategy.

If standing water is the sole water source for livestock, then sampling of the water is highly recommended because the risk of cattle consuming toxins or coliforms is increased.

In general, cattle tolerate high coliform concentrations in drinking water without any effect on production or reproduction. Thus the major issues, in terms of cattle health, would be related to nitrates or chemicals.

Water samples can be collected in 16 oz. disposable water botte bottles. Once a sample is taken, it can be sent to a diagnostic lab. Iowa State University (ISU) Diagnostic Lab is one that can conduct the needed analysis:

Veterinary Diagnostic Laboratory
Iowa State University
1850 Christensen Dr.
Ames, IA 50011-1134

The samples can be submitted using the “Analytical Services Submission Form On the 2nd page of this pdf form, select “Water Quality Panel”. This panel would include nitrates, total dissolved solids, sulfates, and coliforms for a cost of $40. The cost to do a screen of all chemical contaminants is $150 A panel for heavy metals is also available and costs $50.

Refrigerate the samples until you are ready to send them to the laboratory; water sampled for bacteria analysis must reach the laboratory within 30 hours of collection to produce accurate results.

One can expect a couple weeks for results to be returned upon submission. For more details, direct questions to Steve Ensley, KSU Clinical Toxicologist at or 785-532-4287.