Hard Water and Soap: Why You Get Soap Scum

If your soap barely lathers and your shower walls get a chalky film, hard water is the likely reason.

What hard water is

According to the U.S. Geological Survey, hard water has high levels of dissolved calcium and magnesium, while soft water has low levels.

Why soap and hard water clash

Those minerals react with soap to form soap scum, an insoluble residue. That reaction uses up some of your soap, so you get less lather and need more water to rinse. Scum can also cling to skin, hair and shower surfaces.

Signs you have hard water

• Soap lathers poorly.
• A film on glass shower doors and tiles.
• Hair feels coated after washing with soap-based shampoo.
• White spots on dishes.

What helps

• Rinse well and use a little more water.
• Try a syndet bar or pH-balanced shampoo bar, since detergents are less affected by hard water than soap. See shampoo bars vs liquid shampoo.
• Squeegee or wipe the shower after use to stop scum building up.
• A water softener replaces calcium and magnesium with sodium, so soap lathers more easily.

How to find out how hard your water is

• Check your water report: most U.S. public water suppliers publish an annual water quality report (sometimes called a Consumer Confidence Report) that often lists hardness.
• Use test strips: inexpensive hardness strips give a quick reading at home.
• Watch for clues: limescale on kettles and faucets is a reliable sign.

The USGS groups water by the amount of dissolved calcium carbonate: soft water has low levels, and moderately hard, hard and very hard water have progressively more.

Cleaning off soap scum

1. Prevent it: squeegee glass and wipe tiles after each shower. This is the easiest fix by far.
2. Weekly clean: spray a diluted vinegar solution on glass and tile, leave for a few minutes and wipe. Rinse well. (Do not use vinegar on natural stone such as marble, which acid can damage.)
3. Stubborn buildup: a paste of baking soda and water with a non-scratch scrubber, followed by a rinse.
4. Keep soap off surfaces: a draining soap dish stops a sticky puddle forming under the bar.

Hair care in hard water

Hard water is the main reason people give up on soap-based shampoo bars. If your hair feels waxy or coated after washing with soap, try a diluted acidic rinse (a small amount of vinegar or lemon juice in a cup of water), rinse very thoroughly, or switch to a pH-balanced syndet bar. Many shower filters are marketed for hard water, but check what they actually remove, because not all reduce calcium and magnesium.

Skin in hard water

Some people notice drier skin in hard-water areas, partly because soap residue lingers. Rinse well, keep showers short and lukewarm, and moisturize after washing. If you have eczema and notice flares, mention your water to your doctor.

Should you avoid natural soap if you have hard water?

No, many people with hard water use true soap happily. Just expect less lather, rinse well, and wipe surfaces regularly.

The science behind lather: how does soap clean.