Interpreting Drinking Water Tests for Dairy Cows
NOTE: While various studies have been done to link water quality problems with livestock health or performance, specific conclusions on the concentrations where water pollutants cause problems often vary between studies. This fact sheet attempts to provide the best consensus on levels of concern for common pollutants but readers should visit the references listed on page 3 to learn more about the range of conclusions for each pollutant.
Few studies have linked water pH with any livestock health or performance issues. Adams and Sharpe (1995) suggested that water pH should fall between 5.1 and 9.0 based on experiences with dairy herds in Pennsylvania. They suggested that acidic water with a pH less than 5.1 may increase problems related to chronic or mild acidosis while water with a pH over 9.0 may result in problems related to chronic or mild alkalosis. Other authors have recommended a more strict pH range between 6.0 and 8.5 largely based on field observations rather than controlled studies. We suggest that water supplies with a pH below 6.0 or above 8.5 should be further evaluated where unexplained herd health or performance issues occur.
Total Dissolved Solids (TDS)
TDS is a sum of all of the inorganic contaminants in water. Drinking water with less than 1,000 milligrams per liter (mg/L) of TDS is ideal for dairy cows. Levels of 1,000 to 3,000 mg/L are usually satisfactory but may cause various performance issues depending on the exact contaminant causing the elevated TDS. Levels above 3,000 mg/L are more likely to cause poor tasting water that may result in reduced water intake and milk production again depending on the exact pollutants causing the high TDS concentration. Overall, water with a TDS above 1,000 mg/L has the potential to cause livestock problems and should be tested for all major water minerals, salts and metals.
Nitrate-Nitrogen and Nitrite-Nitrogen
Nitrates can occur in both feedstuffs and water and the risk is additive. For this reason, livestock producers should be aware of nitrate levels in both the drinking water and food. Although nitrate-nitrogen levels above 10 mg/L in drinking water can be harmful to human infants, research has shown that livestock can generally tolerate slightly higher nitrate-nitrogen concentrations. Drinking water concentrations above 20 mg/L as nitrate-nitrogen could present herd health issues depending on concentrations in food (which should be carefully evaluated). Nitrate-nitrogen levels over 100 mg/L in drinking water represent a higher risk for fertility and other health issues again depending on the intake from feed.
Hardness, Calcium, Magnesium
Hardness is mostly a measure of the calcium and magnesium in water. Hard water causes many aesthetic problems with the use of the water, such as restricted water flow from mineral deposits, but it generally does not adversely affect cows. Extremely high concentrations of calcium or magnesium above 500 mg/L should be included in ration formulation.
Sodium in water is rarely problematic for dairy cattle but sodium concentrations should be included in the ration formulation if levels exceed 20 mg/L.
Iron and Manganese
Iron and manganese are very common pollutants that can occur naturally in groundwater or from nearby mining activities. Both cause severe staining and a metallic taste to water resulting in reduced water intake and reduced milk production. Iron levels above 0.3 mg/L and manganese concentrations exceeding 0.05 mg/L are sufficient to cause unpleasant tastes in water that may cause reduced water intake and milk production.
Chloride in water may occur naturally from deep brines or as a result of various activities such as gas and oil well drilling or road deicing. Chlorides above 250 mg/L can impart a salty taste to water which could result in reduced water intake and milk production. Water supplies serving herds with performance problems should be tested for chlorides as a potential explanation. High chlorides should also be considered when formulating diets to prevent an excess which could be detrimental to rumen function.
Various research studies have produced differing levels of concern for sulfate in water for livestock. Sulfate concentrations below 1,000 mg/L are generally thought to be safe for adult animals but some authors have suggested limits as low as 500 mg/L. High sulfate has been linked to reduced milk fat and increased needs for selenium, vitamin E, and copper. Over time, some animals become acclimated to elevated sulfates in water resulting in reduced symptoms.
Copper usually occurs in water from corrosion of metal plumbing components. It may also be elevated in mining areas or from treatment of ponds with copper sulfate algaecides. Copper levels above 1.0 mg/L may cause a metallic taste resulting in reduced water intake and milk production. High copper concentrations may also cause liver damage.
Coliform bacteria occur in all surface waters (streams, ponds, etc.) and many groundwater wells. Coliform bacteria in wells usually come from surface water contaminating the well or from insects under the well cap. Water used for washing equipment, udders and teats should have zero total coliform bacteria per 100 mL of water.
There is less certainty about the effect of coliform bacteria on drinking water for dairy cows. Recent research on over 200 dairy herds in Pennsylvania was unable to show a correlation between bacteria and herd health issues. Also, the concentration of coliform bacteria is strongly related to the location where the water is collected. Water samples from drinking troughs may have large concentrations of coliform bacteria, especially if the troughs are cleaned infrequently. Samples collected at drinking areas compared to the source well water will indicate the need for better sanitation. Clean and sanitize drinking cups, bowls, and tanks daily to reduce bacteria loads. Use a raised base around bowls or tanks to reduce manure contamination of water.
E. coli Bacteria
E. coli bacteria occur from direct contamination by animal or human waste. As such, the occurrence of E. coli bacteria is much more serious than total coliform bacterial contamination. E. coli bacteria can be found frequently in bowls and troughs due to direct contact with animals. Frequent cleaning of water locations can minimize exposure to E. coli or other fecal bacteria in water. It is recommended that E. coli or fecal coliform bacteria should be absent from drinking water for cattle.
The PDF file linked below contains a table which summarizes common water quality parameters for livestock in Pennsylvania. Included in the table are the human drinking water standard, median concentrations typically found in groundwater in Pennsylvania, and levels potentially causing livestock health or performance problems. Parameters with a “—” in the final column indicate those with a lack of consensus among research studies about any definitive problem in drinking water for livestock.
Various other metals in water such as aluminum, arsenic, boron, cadmium, chromium, cobalt, lead, mercury, nickel, selenium, vanadium and zinc may affect herd health or performance. Consult the references below for more information about these metals and the data in the table.
Sources of More Information
- Adams, R.S, and W.E. Sharpe, 1995, Water intake and quality for dairy cattle, Penn State Extension, DAS 95-8, 7 pp.
- Beede, D.K. 2006. Evaluation of Water Quality and Nutrition for Dairy Cattle, 2006 High Plains Dairy Conference, 24 pp.
- Linn, J. and M. Raeth-Knight, 2010. Water Quality and Quantity for Dairy Cattle, University of Minnesota, 5 pp.
- National Research Council, 2001. Nutrient Requirements of Dairy Cattle, 7th Rev. Ed. National Academy Press, Washington, D.C.