Water is the most vital component of the equine diet, but it is often overlooked when considering your horse’s nutritional needs.

Hydration influences several aspects of horse health, including exercise tolerance, digestion, and temperature regulation. Not only do you need to ensure that your horse drinks enough water, but also that your horse has good quality water available.

Testing water quality helps to determine whether your horse’s water supply is safe for consumption and whether you need to consider a water treatment or filtration system.

A water analysis will also tell you about the mineral levels present. This can help you address any potential dietary imbalances caused by water intake.

To learn more about water analysis for horses and how horse owners can promote healthy hydration with correct management, continue reading below.

The Importance of Hydration for Horses

Water makes up roughly 70 percent of an adult horse’s body. It is involved in nearly every bodily function, from circulation to digestion and joint lubrication to waste filtration. [1]

A lack of water is an imminent threat to your horse’s vital systems. Dehydrated horses can suffer serious problems such as lethargy, gut impaction, colic and impaired kidney function. [2][16]

Water Intake

An average 1,100lb horse with an idle lifestyle requires 6 to 9 gallons of water daily to support normal bodily functions in thermoneutral conditions. [3]

Higher temperatures and heavier workloads can increase daily intake requirements to 12 to 18 gallons. Lactating mares also need extra water to support milk production. [4]

A horse’s diet also affects water consumption. Horses on pasture get significant amounts of water from eating lush green grass with high moisture content. [5]

If a horse has a high protein diet, it must excrete excess nitrogen via urine. These horses will drink more water to support the increased urine production. [5]

Some environmental conditions can reduce voluntary drinking. For example, some horses drink less water in winter if the water temperature is below 45 degrees Fahrenheit. [6]

Water impurities can also cause reduced intake. Water often contains minerals, bacteria, algae, and other dissolved solids. These substances can impact palatability and voluntary intake.

Preventing Dehydration in Horses

Horses should have free access to clean, fresh water at all times. [3]

Most horses prefer water between 45 degrees and 65 degrees Fahrenheit. However, evidence suggests that providing lukewarm water with a temperature of 68 degrees Fahrenheit promotes better hydration in cold weather. [6]

Adding plain loose salt to a horse’s diet can also encourage hydration. Salt is a source of sodium, which is an essential mineral that plays a role in stimulating the horse’s thirst response and maintaining fluid balance. [4]

You can also support hydration by feeding your horse an electrolyte supplement in hot weather or after exercise.

Another way to provide water in your horse’s diet is to soak hay or feed. Providing access to grass pasture where available can also increase water intake. [5]

Can Horses Drink Too Much Water?

Yes, horses can drink too much water, but dehydration is much more common. [3] Excessive water intake is most common in horses with PPID/Cushing’s disease or other health conditions that cause abnormal drinking behavior. [7]

Drinking too much water stresses the horse’s kidneys and can interfere with electrolyte balance. [2] However, most healthy horses won’t drink beyond normal limits.

Testing Water Quality

Whether the water source on your horse’s farm is a private well, public water supply, pond, lake, or river, water quality tests are always recommended. [18]

A water analysis looks for physical properties, microbes, mineral levels, and toxic compounds. Testing water regularly during different times of the year and changing periods of rainfall is suggested for accurate results. [8]

Physicochemical properties impacting palatability include water pH, hardness, and salinity. Salinity measures salt concentrations, while hardness refers to the amount of magnesium and calcium in the water.  [12]

Water can also contain other minerals that impact the overall nutrient ratios in a horse’s diet. Water with high levels of bacteria or toxic substances is unsafe for horses to drink. [8]

The following are some of the values usually reported on your water quality analysis.

Total Bacteria Count

The total bacteria count on a water analysis is reported in colony-forming bacterial units (CFU).

Water consumed by horses and other livestock should have a total bacteria count of less than 200 CFU per 100 ml. [9]

Drinking water analyses measure the concentration of two categories of bacteria: total coliforms and fecal coliforms. These bacteria indicate the presence of sewage and animal waste. [9]

Water with a high total bacteria count may have high nitrate levels. Nitrates and bacteria can enter the water supply through surface runoff contaminated with fertilizer. [18]

Total Coliforms

Total coliform represents a large group of bacteria found in the environment, most commonly in the soil.

Total coliform counts may be elevated in water sources affected by surface water runoff. Well water can also be contaminated by microorganisms when structural issues such as broken caps allow debris, insects, or rodents in. [19][20]

Ruminant studies report that coliform counts higher than 1 bacterium per 100 ml cause diarrhea in calves, while older cattle can tolerate water with 20-50 coliforms per 100 ml. [9]

Horse owners could benefit from more research on the effects of acceptable total coliform concentrations in equine subjects.

Fecal Coliform

The fecal coliform group includes bacteria commonly found in the intestines of warm-blooded animals. [21] E. Coli is a well-known fecal coliform.

This type of bacteria in a water sample can indicate recent fecal contamination, resulting in a greater risk of pathogen exposure. [21]

Horses should not consume any water that contains fecal coliforms unless it is adequately treated. [3]


Nitrate is a naturally occurring form of nitrogen found in fertilizers. Hindgut bacteria can convert nitrates to nitrite, a potentially toxic compound. [22]

Nitrites harm horse and human health because they can limit oxygen transport in blood by displacing oxygen on the hemoglobin molecule. [10]

Horses have more resistance to nitrate toxicity than cattle, but contaminated water can still cause gastrointestinal distress. [9]

Water with nitrate levels of 400 mg/L is generally safe for horses. [23]


Sulfates are sulfur-containing mineral salts that are toxic for horses in high concentrations. [11]

Animal and plant matter decay produces this compound. Some sulfates are also by-products of industrial manufacturing. [11]

While horses have a high tolerance for sulfur, case studies have linked excessive sulfate levels to diarrhea outbreaks and sudden death. [11]

Some areas in North America have water with naturally high levels of sulfur characterized by a rotten egg smell. Unless your water analysis reports concerning sulfate concentrations, slightly elevated sulfur levels generally only impact palatability. [24]


Hard water contains high levels of dissolved minerals. In addition to sulfur, other minerals found in some water sources include calcium, magnesium, iron, manganese, fluoride, and sodium. [17]

Hardness is determined primarily by the amount of calcium and magnesium in the water sample. If you suspect your water source is hard, a water analysis can help determine if these concentrations will impact your horse’s health. [12]

Many horse owners have concerns about sources of iron in the equine diet. While most water won’t contain enough iron to risk iron toxicity, high levels of this mineral impact the absorption of other minerals, such as zinc and copper.

Recent research suggests that horses with prolonged exposure to high levels of iron in water, hay, or grass can develop liver problems due to chronic iron overload. [13]

Water pH

The acidity or pH level of your water supply can impact the palatability of water for your horses. [14]

The pH scale measures how acidic or basic a substance is on a range from 0 to 14. Pure water has a natural pH of 7, while a pH of less than 7 indicates acidity.

In one study, horses offered water from a control bucket with a pH of 7.5 drank more than horses offered more acidic water with pH levels of 5.0, 3.6, and 2.9. [14]

Total Dissolved Solids

Total dissolved solids, or TDS, is the total concentration of all substances and contaminants in a water panel test. [17]

The safe upper limit for equine water sources is 6,500 ppm TDS. Fresh water has a TDS below 1,500 ppm, and water is considered saline if the TDS exceeds 5,000 ppm. [15]

Water Management for Horses

Water quality analysis is an important component of managing your horse’s health. Testing water can ensure it is safe for consumption and identify any root cause of palatability problems.

Depending on the results of your water panel test, you may need to implement management strategies to preserve or improve water quality and promote hydration.

Clean Water Sources

Horse owners should keep horse waterers, water buckets, and tanks as clean as possible. Stagnant water and dirty water troughs can threaten your horse’s health by allowing algae, bacteria, and other microbes to grow. <