Should I Worry About the Hardness of My Horses' Water?

Should I Worry About the Hardness of My Horses' Water?

Water hardness, a term associated with the amount of calcium and magnesium in water, likely does not affect horses' diets.

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Q. My local water company has recently announced that our new community water source (underground wells) is “hard” water, with higher levels of calcium and magnesium than were in our previous water. At a public meeting this week, one of the residents complained that her horses are acting “differently” since the introduction of the new water. My horses seem to be drinking a little more than they did previously. I feed a 14% protein/6% fat pelleted local feed and free-choice mixed-grass hay, and my horses have free-choice access to pasture and white salt and mineral blocks. 

Do I need to worry about the change in water or the additional source of calcium in their diets?

Liz, Nashville, Tennessee


A. “Hardness” is term that is often associated with the amount of calcium (Ca) and magnesium (Mg) in water. In many cases the calcium and magnesium in water sources are associated with a particular area’s geology, so water from one region might be naturally higher in calcium and magnesium (and, thus, “harder”) than in another region. You can remove calcium and magnesium from water using a water softener. Many people choose to use a water softener to reduce their water’s hardness because they believe that softened water cleans better and leaves less residue on dishes or on fixtures. 

In this case it appears that a municipality has either changed water sources or perhaps has reduced the amount of softening it performs on the water. You have inquired whether the increased hardness could be a problem for horses. The first concern with a change in water source is whether the horses discriminate against it and reduce water consumption. If you did not observe a decrease in water intake, then that concern is minimized. 

The next concern could relate to the amount of calcium and magnesium that horses could be consuming from the water. The water company has said that the water is “harder,” but without a water analysis it is difficult to know exactly what that means: a little bit harder or a lot harder? Some of the references I found indicated that hard water could contain as much as 35 mg of Mg per liter of water, or as much as 60 mg of Ca per liter of water. Depending on the season of the year and the amount of moisture in other feeds, an idle 1,000-pound mature horse will drink 20 to 50 liters of water a day. At the highest intake rate (50 L) this hard water would provide 3 grams of Ca and 1.75 grams of Mg per day. Is that a large amount? Just 22 pounds of an average timothy hay will provide about 30 grams of Ca and 20 grams of Mg per day. So, the contribution from the water is very small, even in this example, which would involve fairly hard water. If the change in hardness is small, then the amount of Ca and Mg contributed by water would be smaller. 

I find this to be an interesting question because some horse people prefer nonsoftened water for their horses, believing the minerals in the water are beneficial. There is no evidence for this that I know of, but there is also no evidence I know of that contradicts that opinion either. It may be important to horse owners to understand whether the increased hardness originates from using a new source or if it is due to a change in the water treatment process. In many cases water is softened using an ion exchange process, which sounds complicated but just means that the process exchanges Ca and Mg ions for sodium ions. So, softened water could be higher in sodium than unsoftened water. If horses have access to a salt block, then a lower sodium content in the new water is likely not an issue. 

Finally, water hardness is just one part of water quality. It does not estimate other minerals, compounds, or organisms that might be in the water.

About the Author

Laurie Lawrence, PhD (equine nutrition)

Laurie Lawrence, PhD, (equine nutrition), is a professor in the University of Kentucky's Department of Animal Sciences.

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