How Water Hardness Impacts Soap Performance

Have you ever noticed that your skin feels sticky or tacky after rinsing off your body?  

The reason for this is due to soap scum.

While the name sounds downright disgusting, soap scum is a natural reaction that occurs when the minerals in your water interact with a bar of soap.  

If you have a high amount of calcium and magnesium ions in your water, also known as hard water, soap scum will occur.  However, if you have a low concentration of minerals, then soap scum won’t occur.

What does this mean for the performance of your bar of soap?


  • If you have hard water: This will require more effort to generate a lather.  However, rinsing off your body will be significantly easier.  You’ll know when your body is rinsed off as it will no longer feel slick or smooth; instead, it will feel tacky or sticky.
  • If you have soft water: This requires nearly zero effort to generate a sudsy or thick lather.  When rinsing, you will need to use much more water to get rid of that smoother and almost slimy texture from your skin.

The U.S. Geological Survey (USGS) put together an excellent summary of the properties of soap and how it reacts to the skin if you want to learn more

You’ll know if you have hard water based on the properties of your soap or simply by inspecting your bathtub or shower stall.  If you see residue or grime of soap on the surface, then you have hard water.

What is considered to be hard water?

Hard water contains a higher amount of calcium and magnesium ions than average.  Per the USGS, water hardness is classified into the following categories:

0 to 60 mg/L (milligrams per liter) as calcium carbonate is classified as soft; 61 to 120 mg/L as moderately hard; 121 to 180 mg/L as hard; and more than 180 mg/L as very hard.

Where is hard water in the United States?

The USGS put together a great map on water quality from domestic wells across the United States.  Should your house or apartment rely on well water, you can quickly see what the hardness level is in your area:

Quality of water from domestic wells in the united states

Now, if you don’t have well water, read on:

The hardness of city water varies

Just because you live in a city doesn’t mean you have soft water.  Public municipalities vary in their water treatment processes.  Some cities may soften the water while others may not.  

Additionally, larger cities such as New York rely on multiple water sources.  Per, they have stated the following:

New Yorkers receive their tap water from upstate reservoirs in the Catskill/Delaware watershed, the Croton watershed, or a blend of both sources. Water from the Croton watershed is considered “moderately hard,” while water from the Catskill/Delaware watershed is considered “soft” or “slightly hard.” Citywide, the average hardness is about 1.8 grain/gallon (CaCO3). In areas of the City where Catskill/Delaware and Croton Water supplies are blended, the hardness can reach 7 grain/gallon (CaCO3), which is considered “moderately hard.”.

So even where you live in a large city could result in different water hardness levels.

The takeaway: Check with your local municipality if you have questions about the water source and hardness levels.  

What are water hardness testing kits?

Water hardness testing kits can be found at your local hardware store and are pretty cheap.  For under $10, you can get about 100 paper strips to test your water hardness.  Typically containing a color scale, they can give you an idea of the hardness of the water in under a minute.  

Am I stuck with slimy or tacky feeling soaps forever?

It depends.  If you are in an apartment, high-rise, etc., then there is little that you can do. However, if you are in a house and have hard water, consider installing a water softener.  They are under $2,000 for the unit (including installation costs).  Water softeners can give you instantly softer water for both drinking and bathing.

We double-checked to see if shower filters could work as a temporary or low-cost alternative.  However, shower filters target chlorine and chloramines rather than minerals – so there will not be a noticeable impact on soap performance.

Will hard water and soap scum ruin my skin?

Let me be straightforward; I’m not a dermatologist.  I tried to do some research on this for you and was left with more questions than answers.  

Here’s what I found out:

I was unable to find a single research paper that supported that soap scum impacts the texture or healthiness of the skin.  

The only potential answer was that soap scum might cause dryness, itchiness, and clogged pores.  However, this was from a company that sold water softeners – so take that with a healthy dose of skepticism.

Personal thoughts: if your skin is dry, itchy, or irritated, it may just need some lotion to help it retain moisture.  Use common sense here and make adjustments in your grooming routine as necessary.  Of course, speak with your doctor or dermatologist if you have further questions.

Do certain soaps help balance the finished results?

Honestly, it’s a little bit of trial and error as the hardness of water will vary from house to house.

Even when testing several different soaps bars, we found that the ingredients can make a noticeable impact on the skin’s texture while rinsing.  

Oil-rich natural soaps, such as Dr. Bronner’s Pure-Castile Bar Soap, weren’t nearly as sticky or tacky feeling upon rinsing compared to, say, a Dr. Squatch or Duke Cannon soap.  

Additionally, mass-produced soaps from large brands are designed to work for all water types.  

Final Thoughts

This was a fascinating topic to research as there is so much variability in water hardness and soap composition. We truly hope that the information we covered today gives you a better idea of what happens when washing your body.

Adam Williams

As the lead editor of Tools of Men, Adam loves men's grooming products. Particularly of interest is managing facial hair and perfecting the art of the modern man's skincare routine. His work has been featured or quoted in several publications, including New York Magazine, Vice, Sharpologist, MIC, Elite Daily, and more. When Adam isn't working, he enjoys spending time with his two little kids who keep him both on his toes and young at heart.

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