What is Hard Water?

If you are reading this, it is assumed that you want to ‘go deeper’ into an understanding of hard water, why water is considered ‘hard,’ what minerals make water hard, and what should be done about hard water at each tier of hardness. You will notice that this page delves deeper into the science world as there is a lot of science that goes into the hardness of water and into softening it. As a result, we do want to warn you, the science discussion in this document is at a somewhat higher level than some of our other pages.


Hard water affects about 85% of households in the United States. Hard water refers to water that contains calcium, magnesium, and other minerals (like manganese). As all of these chemicals are white or gray in appearance, this is why deposits will appear to be white in nature around faucets. Hard water affects our homes and our lives in several ways. It can produce deposits in and around our faucets, water spots, shower doors, and clothing. It can reduce the life span of appliances as they have to work harder in order to offset the mineral buildup, and it can clog drains, filters, faucets and galvanized steel pipes. Hard water is particularly pertinent when talking about cleaning, as it reduces the power of our cleaning products and detergents because the minerals chemically interact with surfactants, preventing them from properly targeting soils. Hard water will not affect your health – you can drink it, use it in cooking, etc. without cause for concern (it can affect taste and yeast or bacterial growth, which is relevant if you are making yeast bread or other fermented foods, but these things are not related to cleaning).


If you suspect that you have hard water, you should measure your water with a test strip. Many water reports will have levels from years prior, but most water changes in hardness with the amount of rainwater, the seasons, and/or the location of the source that your water company draws from. For this reason, we encourage people to test their water for themselves if they are having difficulty with their laundry or cleaning. You can get a test strip that has a measure of water hardness from most pet stores near the exotic fish, a pool supply store, some hardware stores, and in these sections of your local SuperCenters. Alternatively, you can take a water sample to your local pet store and have them test it. Be sure to get a number from them, rather than just ‘hard’ or ‘really hard’. Water hardness should be tested in both hot water and in cold water, as your hot water heater can ‘kick up’ minerals that have been deposited and increase the mineral deposits in your hot water.


Example of a Water Hardness Test


All minerals affect water hardness similarly. So, a single molecule of magnesium has the same effect as a single molecule of calcium. Therefore, if you knew the exact amount of calcium, magnesium, and other minerals in your water, you could add the concentrations together (in molecules or moles per equal amount of water) to calculate total hardness. However, we most often see water hardness measured by mass of the mineral per mass of water. Since each mineral has a different molecular weight, we need to convert all the concentrations to the same unit. Parts calcium carbonate (CaCO3) per million parts water is the standard unit that we convert to, sometimes written as PPM as CaCO3. This measurement includes the contributions of all minerals, it’s just converted because calcium carbonate is the chemical molecule that most often contributes to water hardness.


Water hardness is measured in parts per million (PPM) or grains per gallon (GPG), where the first number (the parts or grains) refers to the minerals (converted to equal units based on the molecular weight of calcium carbonate), and the second number (the million or gallons) refers to water.


In general, water that is 17-60 ppm (1-3.5 gpg) is considered slightly hard (soft for the purposes of cleaning, even though it does contain some minerals), 61-120 ppm (3.6-7.0 gpg) is considered moderately hard, 121-180 ppm (7.1-10.5 gpg) is considered hard, and 181 ppm and over (10.6 gpg and over) is considered very hard.


You don’t need to take any action if your water is slightly hard with most detergents. If your water is moderately hard, you may want to add 1/4 cup of Borax water softener to your laundry. If your water is hard, you may want to add 1/2 cup of Borax water softener to your laundry. If your water is very hard, you may want to add 3/4 cup + of Borax water softener to your laundry. Water that is harder than 180 ppm, 300 ppm to 1000 ppm will want to either add 1 cup of Borax water softener or look into Calgon water softener and add a full cap. Calgon targets a broader spectrum of minerals and can be used in harder water for this reason. Water that is 500 ppm+ should look into whole house water softeners, eventually, when it is financially reasonable to do so, as it will save time, energy, and wear and tear on appliances.


Sightly Hard
Moderately Hard
 Very Hard
Exceptionally Hard
Above 300
Above 17.5
No action
Most detergents will be
able to compensate for this level of hardness.
1/4C Borax
1/2C Borax
3/4C+ Borax
1C Borax or 1 Cap Calgon
*Authors note: Articles and resources that I read will have no category as high as this table. I am adding ‘Exceptionally Hard’ based on my personal experience with hard water and my experience helping others with their laundry or cleaning.


The above are *general guidelines* for the hardness level of your water. However, not all detergents are created equal. Free and clear and plant-based detergents will need an added water softener at a lower level of hardness. This is because the nature of the surfactants used is different. The surfactants are not simply less in free and clear and plant-based detergents, they are different surfactants completely. For instance, Tide(R) and Persil(R) are both considered to be more effective detergents (and more costly) because of the variety and amount of surfactants contained in them. Tide and Persil both have approximately 25% surfactant in them, referencing their MSDS / SDS. If you are having more trouble with your laundry or cleaning than appears to be normal, we recommend following these steps:
  1. Clean your machines to remove the mineral buildup that may be present, “How to Clean Your Machines.”
  2. Test both your hot and cold water. (See “Testing Your Water Hardness“)
  3. Begin adding the minimum amount of water softeners necessary for your level of water hardness.
  4. Evaluate your detergent.
    • Free and clear and plant based detergents are inherently weaker due to the type of surfactants that need to be used.
  5. Evaluate your wash routine.
    • Are you filling your machine the right amount? Not too little? Not too much?
    • Are you using enough detergent?
    • Is your spot treatment working? Does it target the stains that you regularly see?
    • Have you tried adding an enzyme additive? (Biz or OxiClean White Revive have enzymes).
  6. Contact an Admin here or on our Facebook group for problem solving help.


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By Amanda Perez