Evaluating Water Quality for Dairy Cattle

By Brad Oldick, Ph.D. Dairy Nutritionist

Water quality is becoming a greater issue for dairy producers as they continue to grow and put additional stress on their water resources.  Water quality within a water source is not necessarily a constant over time.  Pulling additional water from a well, weather patterns and fertilizer application are all items that can influence water quality within a well.  Some producers have found that managing water quality is better left to local municipalities and have started purchasing water for their cattle rather than pulling water from a private well.  For producers using a private well, a water quality control program should be in place.

It is difficult to establish a water quality program and determine it’s effectiveness if you do not establish a way to measure water intake.  This can be done relatively easily with in-line water meters that measure only the water supplied for drinking.  Measurements should be taken for at least 7 to 10 days to account for day-to-day variation.  Once water intake is established, it should be compared with expected intake and factors limiting intake evaluated.  Keep in mind that there are many factors other than water quality that can limit intake.  Although these are not the focus of this Nutrition Note, some factors include cleanliness of water tanks, water supply (gallons delivered per minute), stray voltage and water space/accessibility.

Cows can display several signs of inadequate water intake including:

  1. Sudden drop in milk production (if the factor limiting water intake occurs suddenly).  Problems that arise slowly over time do not cause this sudden drop; therefore, you do not need to see this symptom to have a water quality issue.
  2. Infrequent drinking.
  3. Firm manure.
  4. Low urine output.
  5. Drinking urine.
  6. High blood packed cell volume (PCV) – over 38% average PCV in a group of cows.  This is an indicator of dehydration.

Water analysis and evaluation can become quite complex.  There are many elements that can be tested for in water (e.g., total dissolved solids (TDS), sodium, calcium, magnesium, chloride, sulfates, nitrates, iron, manganese, copper, hardness, total coliforms, arsenic, barium, cadmium, cobalt, lead, mercury, aluminum, fluorine, & pesticides).  However, an initial water analysis does not need to be this complicated and should focus on a few key components that are the most common factors causing decreased water quality. 

Many certified water testing laboratories offer a “livestock suitability” package that includes TDS, sodium, calcium, magnesium, chloride sulfate, nitrate, iron, manganese, copper and hardness.  The key components to monitor routinely will be addressed below:

  1. Total Dissolved Solids (TDS):  This is a measure of the sum of all the inorganic material that is in the solution within the water.  High TDS does not always indicate the water is not suitable for livestock.  There are some solids (i.e., calcium and magnesium) that can be high in the water without detrimental effects on livestock.  Target levels for TDS are 500 – 1000 ppm.
  2. Hardness:  This is a measure of the amount of calcium and magnesium dissolved in the water.  Hard water is often a problem when cleaning milking equipment, but it does not appear to impact performance in dairy cattle.
  3. Sulfate:  High sulfate levels will cause decreased water intake and decreased milk production.  Also, because sulfur is an anion, high levels will reduce overall cation-anion difference.  This will have a negative impact, particularly in fresh cows, resulting in increased metabolic disease.  Target levels for sulfate are 250 – 500 ppm.  A thumb of rule for anions in the water is to keep the sulfate + chloride concentration below 1000 ppm.
  4. Chloride:  See sulfate (above).  Target levels of chloride are 250 – 500 ppm.
  5. Iron:  Importance is secondary only to sulfate and chloride.  It causes reduced water palatability and promotes growth of black slime in water tanks (this is the result of bacterial growth).  Iron in water is nearly 100% available to the animal (iron in feed is generally only about 10% available).  High iron can bind copper and zinc, making them unavailable to the animal.  Once absorbed, high iron levels promote free radical production, decreased immunity and increases the incidence of infection, particularly in fresh cows.  Target levels for iron are 0.3 ppm or less.
  6. Manganese:  It causes off flavor and decreased water intake.  Target levels for manganese are 0.05 ppm or less.
  7. Nitrate:  The most common source of nitrate in water is fertilizer run-off.  High nitrates do not appear to impact milk production, but decreased reproductive performance has been reported.  Target levels for nitrate nitrogen are 20 to 25 ppm or less.
  8. Copper:  High copper levels in water can cause liver damage.  Target levels for copper are 0.3 ppm or less.

Water quality at a dairy farm is a dynamic component of the operation, much in the same way as forage quality.  To monitor and manage this, water samples should be analyzed quarterly and kept as part of the herd record.  When water quality is identified as a limiting factor, there are many options to help “clean” the water (e.g., carbon filtration, air stripping, chlorination, distillation, cation-anion exchange, filtration, reverse osmosis).  These are all generally quite expensive.  Before considering these options, a reputable supplier should be identified who will guarantee that their system will remove the unwanted components from the water (as measured by an independent laboratory).  Maintenance cost should also be considered.  Finally, the return on investment should be estimated before spending large sums of money to manipulate water quality.