Connection between hard water and urinary crystals in cats?

There are indications, based upon a study carried out by a large pet medical insurer, that there is a connection between urinary tract health problems, particularly crystals in the urine, and hard water. BUT there are counterarguments and this is only one study. I can’t find others which supports this. Note: this page was first written in 2016. It has been updated May 2023 because the topic has returned in news media online. I have added to the page.

Does hard water harm pets?

However, the finding may be quite significant IF the connection can be confirmed. A while ago Eliza Black-Taylor wrote about the possibility of tap water causing cat health problems. This is a follow-up to that article.

Struvite Crystals
Struvite Crystals. Photo: Cuyahoga Falls Veterinary Clinic
Until September 7th I will give 10 cents to an animal charity for every comment. It is a way to help animal welfare without much effort at no cost. Comments help this website too, which is about animal welfare.

The leading provider of medical insurance for dogs and cats, Trupanion, released a report on seventh April which identified a possible connection between urinary health problems amongst pets and hard water ratings in America per the Environmental Protection Agency (EPA).

For example, in Tampa, Florida where the water is said to be extremely hard, they found that they were paying out 10 times as many claims for crystals in urine amongst male cats compared to payments made in respect of male cats living in soft water areas.

The insurance company says that hard water contains more calcium and magnesium. Also hard water can cause health problems in humans. Male cats living in “extremely hard water” areas suffer a much higher incidence of urinary health issues, particularly crystals found in urine which is described as “crystalluria”. Overall they were three times more likely to have urinary complications compared to male cats in areas where the water was less hard and described as “slightly hard” or “hard” or “very hard”.

With respect to cats, interestingly, they discovered that male cats are 1.5 times more likely to be the subject of a claim for medical treatment with respect to urinary health issues than for female cats.

With respect to dogs, owners of female dogs are 2.5 times more likely to submit a claim for urinary conditions compared to owners of male dogs.

Overall, the urinary tract conditions allegedly affected by hard water include: urinary tract infections, cystitis, urinary obstructions and, as referred to above, crystalluria.

Hardwater ratings in USA (EPA)
Hardwater ratings in USA (EPA)

The map above shows visitors where hard water is found in America. “Extremely hard” water is found in Miami, Chicago, Detroit, Cincinnati, Minneapolis, to name some cities.

Sometimes urinary tract problems can be very expensive to treat. In one case a cat required extensive surgery at a cost of $11,600.

The Chief Veterinary Officer at Trupanion made the point that a further study is required to confirm the connection between hard water and crystalluria. However, should this connection be confirmed, which appears to be likely, then it must have a significant impact on decision-making by pet owners with respect to the quality of drinking water in their households. It would, on the face of it, mean pet owners seriously considering softening the water in their homes across large areas of America because the impact of hard water, on the basis of this initial cross-referencing, on a cat’s health is substantial and it cannot be ignored by any responsible cat owner.

Note: the top picture is for illustrative purposes. I don’t know if struvite crystals are caused by hard water.


This leads me to a counter argument. I have checked Google Scholar and found nothing to support Trupanion’s conclusion (2023). In fact, there are benefits to calcium and magnesium in the diet which is what causes hard water.

The Annals of Internal Medicine website (I don’t know it) says the following:

“Many studies suggest that reduced consumption of calcium or magnesium is associated with an increased risk of developing hypertension and cardiovascular disease. Results of animal studies show that restriction of calcium increases, and supplementation with calcium lowers, the blood pressure of normal and hypertensive rats.”

One scientist (Schroeder, 1960) quoted the saying: “sot water, hard arteries” meaning hard water helps to keep the arteries healthy. Calcium and magnesium are important minerals for life.

2023 – More information

This article was written in 2016 as mentioned. Interestingly, in 2023 an expert has warned of harmful tap water which could make your pet seriously ill they say. The expert is Gene Fitzgerald who works at a company called Best Osmosis Systems (BOS). They are therefore biased in my view because they want to sell more of their systems. I don’t know whether they are referring to the insurance company’s report mentioned on this page which may in itself be discredited but this topic is worth discussing.

Fitzgerald says that the water in our homes could be “slowly poisoning our pets”. A very provocative statement. They told The Mirror newspaper:

Hard water contains high levels of calcium and/or magnesium, for pets, this can be harmful. If a dog drinks too much hard water for too long a period, for example, they can develop conditions such as urinary tract and/or bladder infections, cystitis, urinary obstruction, crystalluria and stone formation”

And they say that hard water can cause health issues in pets such as skin problems, dental issues and digestive issues. They suggest that the reverse osmosis and distillation water softeners are a great solution but these systems contain sodium i.e. salt which can be equally harmful to pets.

Personal conclusion

I’m left with confusion to be honest. There may be something in this in areas where the water is particularly hard. I think that is probably the key point. If water is abnormally hard where you live there is possibly an argument that it should be softened. But under normal circumstances I don’t see enough evidence to support the notion that hard water harms pets.

Does that mean that if you filter out these minerals from tap water you can harm your cat? I don’t know. The point is that there is nothing clear cut here.


2 thoughts on “Connection between hard water and urinary crystals in cats?”

  1. I’ve never had male cats, and have avoided them for this reason. I’ve also read that “softened” water isn’t healthy for cats to drink. Filtered water isn’t necessarily softened as far as I know. I’ve also read that the best water for humans and animals is “structured” water. I used to make structured water in a glass jar with spigot, with something in a net bag called “Pearls”. I wish I could do that now, but I’m in a tiny cramped space with little counter or floor space.

    I’m wondering if any readers use structured water, and their process. I’m also wondering if putting crystals in the water would change the structure. If water is affected by our words, then I would expect it to also be changed to a higher level by crystals.

  2. “With respect to cats, interestingly, they discovered that male cats are 1.5 times more likely to be the subject of a claim for medical treatment with respect to urinary health issues than for female cats.”

    This isn’t exactly new. Male cat’s urethra is much smaller, one vet blog said the difference is like the difference between a milkshake straw and a coffee stirrer. All the articles say that blockage is almost exclusively a male cat problem.


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