Interpreting Drinking Water Tests for Dairy Cows

By Bryan Swistock

Dairy farms rely on good quality water to ensure maximum milk production and herd health. Experience in Pennsylvania has shown that aesthetic pollutants like iron, manganese and hydrogen sulfide, are the most common water-related causes of problems with dairy herds. These pollutants cause tastes or odors that result in reduced water intake and milk production. Other pollutants, such as nitrate or heavy metals, can cause health effects in dairy herds.

A recent research project on 243 dairy farms from 41 counties across Pennsylvania found that 26% of the farm water supplies had at least one water quality issue. Average milk production for these farms was 56 pounds per cow per day, compared to 62 pounds on the farms with good water quality. Interestingly, none of the farms with high milk production (above 75 pounds of milk per cow per day) had existing water quality problems while 32% of farms with low milk production (below 50 pounds of milk per cow) had at least one potential water quality problem.

Routine and inexpensive ($40 to $70) water testing can be used to identify existing water quality issues that might affect dairy herd health or milk production. The Penn State Agricultural Analytical Services Laboratory offers drinking water testing for dairy herds on their Livestock Drinking Water Testing page. The information in this article can be used to interpret these water tests for the most common parameters.

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 article attempts to provide the best consensus on levels of concern for common pollutants but readers should visit the references listed at the end to learn more about the range of conclusions for each pollutant.

pH

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

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

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.

Sulfate

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

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

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.

More Information

Table 1 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.

Effects of Water Quality on Water Consumption

Water quality issues can manifest as health issues in dairy cows or, more often, as reduced water intake. The most accurate measurement of water intake is from water meters installed on lines to drinking devices. Penn State Extension encourages dairy farms to install water meters to evaluate the herd’s water consumption level as an indicator of existing water quality problems. Cows should be prevented from accessing other water sources and meters should be read over a 5 to 10 day period to minimize weather-related differences. Simple water meter measurements provide a good estimate of water use but more accurate measures would include both metered water use and ration water intake from high moisture feed ingredients.

Expected water intakes for various dairy cattle are listed in Table 2. The range of water use for each cow type is related to air temperature and ration moisture content. Note that water use may be above these ranges for air temperatures above 80 degrees F and lower intake may be observed below 50 degrees F.

The large range in water use for lactating is related to more complex relationships with ration moisture content and milk production. Precise water use within this range can be estimated from equations that include ration water intake, dry matter intake, and milk production at ambient air temperatures between 50 and 80 F. Note that drinking water for lactating cows depends on milk production and ration water intake. Requirements for milking cows include water from both drinking and the ration consumed. Ration water intake depends primarily on amounts of ensiled or fresh forage consumed versus dry hay and grains. Water intake is usually considered to be a problem if it varies more than ±15 to 20 percent of expected values.

When water intake is found to be below normal levels, water quality is only one of several potential causes. In some cases, poor water quality can indirectly reduce water intake by clogging water supply lines or reduced water pressure, most often from hard water, iron or slime-forming bacteria. Stray electrical voltage in or near drinking devices can be one cause of reduced water intake. In cases of stray voltage, obvious animal fear of the drinking devices is often noticeable. In less severe cases of reduced water intake, symptoms may be more subtle such as constipated manure, low urine output, infrequent drinking and high packed-cell volume or hematocrit in blood (over 38 percent in a group of dairy cows).

There are rare instances where water intake is excessive causing increased urine production, loose manure or bloated conditions. Excessive water intake can be related to high intakes of salt or sodium bicarbonate. High urine production can be caused by elevated mercury, protein, non-protein nitrogen (i.e. urea) or nitrate intake.

It should be noted that water intake problems for dairy cattle may be multifaceted. In addition to water quality, forage quality, feed management, nutrition, facilities and others may be contributing to the problem and should not be overlooked.