Should you be concerned that hard water will cause kidney stones? What is hard water anyway? Understand if there is a link between hard water and kidney stones. And, how to know if you have hard water and what you can do about it!
What Is Hard Water?
Hard water is defined by a relatively high amount of calcium and magnesium. Hard water also has minerals like aluminum, iron, zinc, manganese and barium, but most of the “hard” comes from calcium. The degree of hard water is measured in “grains per gallon”. All of these minerals end up in our water from soil or rocks. (1)
Hard water is known for making less “lather” when mixed with soap. It can also leave a ring around your bathtub or white residue on appliances like coffee makers or ice machines. Hard water often has a different taste compared to soft water, may leave a residue after you wash your hair, make cleaners less effective and makes water heaters less energy efficient.
Other than these mostly cosmetic annoyances, hard water is not bad for your health. In fact, some studies have linked hard water with lower risk of mortality from heart disease. However, no conclusions can be made from these preliminary studies. (2)
But what about kidney stones? Does hard water cause kidney stones? Let’s first understand how much calcium is in hard water and if that calcium could affect stone risk.
How Much Calcium Is In Hard Water?
The amount of calcium in hard water varies widely depending on location and water source.
The World Health Organization defines hard water based on the amount of calcium carbonate per liter. (1)
- Moderately hard water: 60-120 milligrams calcium per liter
- Hard water: 120-180 milligrams calcium per liter
- Very hard water: more than 180 milligrams calcium per liter
How Much Magnesium Is In Hard Water?
Compared to calcium, there is not much magnesium in hard water. Amounts vary, but usually hard water has around 50mg of magnesium per liter.
Does Our Body Absorb Minerals From Hard Water?
On average, our bodies absorb around 50% of the minerals in drinking water. Surprisingly, minerals from water contribute 5-20% of the total amount of minerals we eat! (1)
The amount of calcium absorbed from hard water is very different between people. Intestinal absorption of calcium is highly dependent on how much calcium your body needs. For example, if your body needs more calcium, it will absorb a greater percentage of calcium from your food. Other factors, such as vitamin D status, also impact calcium absorption. (3)
What Is Soft Water?
On the flip side, soft water is defined as having a low amount of calcium per liter. The WHO defines soft water as having less than 60mg of calcium per liter. (1)
Where Do You Find Hard Water?
Hard water is found all over the world. Water hardness is dependent on the level of minerals in the soil where you live.
Does Hard Water Cause Kidney Stones?
People Without a History of Kidney Stones
Hard water is unlikely to cause kidney stones for most people.
A few small studies have shown that urine calcium goes up after drinking hard water (5) (6). And, high urine calcium is a risk factor for kidney stones. However, studies have not found more kidney stones in people who live in areas with hard water.(7) (8)
If you do not have a history of kidney stones, hard water is unlikely to cause kidney stones.
People With a History of Kidney Stones
If you do have a history of kidney stones, or have high urine calcium, it is probably a good idea to know how much calcium is in your tap water. Drinking a lot of hard water could make high urine calcium worse. (5) (6)
Calcium supplements are associated with kidney stones, whereas eating high calcium foods is protective. (9) Although no research has been done, calcium carbonate in hard water probably acts more like calcium supplements than calcium from food.
Calcium in hard water might be especially concerning given the high fluid recommended for kidney stone prevention. People with kidney stones are often told to drink at least 2 1/2 liters of fluid per day. At these high intakes, hard water could add quite a bit of calcium to your day.
Please note that very little research has been done to determine if hard water causes kidney stones in people who have had kidney stones. So, it is hard to say if hard water is a big contributor to kidney stones. But, I do think it makes sense to be aware of the calcium content of your water. Knowledge is power!
How Do I Know If I Have Hard Water?
You can check the hardness of your water at home with some simple test strips. These test strips* will tell you approximately how much calcium is in your water.
You can also try a fancy home water test kit*, which will give you much more information about your water. This test kit will tell you the specific amount of calcium, sodium and other minerals in your water.
Check With Your City
If your water comes from a city, annual testing is required and the results must be made available to the public. This is a great option because you can see how much sodium is in your water too. Call your city or look online for your water report.
Make sure your city reports the amount of calcium in your water – not all do!
Non-Specific Home Test
You can also do an simple DIY test at home to check calcium and sodium levels in your tap water. Of course, this option doesn’t tell you exactly how much calcium is in your water. But, is a free and easy starting point to see if you need to dig in further.
What Can I Do If I Have Hard Water?
If you have hard water, chances are this is completely fine and will not impact your health.
However, if you have kidney stones and are concerned about the extra calcium, there are a few options.
Note that Brita (or similar brands) filters do not remove calcium or sodium from water.
Buy Bottled or Distilled Water
Distilling water removes all minerals, including calcium and sodium. Distilled water has zero calcium or sodium.
Instead of buying individual water bottles, a more environmentally friendly option is buying gallons of distilled water. Or, you can even purchase large jugs of distilled water and a water dispenser for your home.
Use a Water Softener
In areas that have very hard water, the city or municipality often softens water for you.
If you have well water, you likely have a water softener at home.
Sodium & Water Softeners
Water softening removes some of the calcium and magnesium from hard water. Water softening usually involves swapping each molecule of calcium or magnesium for a molecule of sodium. The harder your water is, the more calcium and magnesium must be removed, and the more sodium is added during softening.
This could be a problem for people with kidney stones. A high sodium diet can cause kidney stones. Usually, the amount of sodium added during water softening is minimal. But, could be significant in some cases.
How Much Sodium is Added During Softening?
The amount of sodium that is added during water softening varies widely. For very hard water, about 150mg of sodium is added per quart. Assuming you drink 3 liters of tap water per day, this is an additional 450mg of sodium (20-30% of the daily recommendation). Less sodium would be added to less hard water during softening.
Your city’s water quality report may tell you how much sodium is in your water. Sodium is usually reported in “parts per million”, which is equivalent to “mg per liter”. You can usually find water quality reports online, or you can call your city.
If you have a water softener at home, this site can help you understand how much sodium is getting added based on how hard your water is.
You can also test your water for sodium yourself with a fancy home test kit*.
How Can I Prevent Kidney Stones?
Chances are, hard water is not the sole cause of kidney stones. Hard water may exacerbate high urine calcium, but is unlikely to be the initial cause.
Although there are many causes of kidney stones, a poor diet is one of them.
Generally, the key parts of a healthy diet for kidney stone prevention are:
- Drinking lots of water
- Limiting sodium
- Limiting added sugar
- Eating the right amount of protein
- Eating lots of fruits and vegetables