I’m frequently asked about why soft water is “slimy”. Some people will tell you that you’re feeling your natural body oils when washing with soft water. Body oils play a VERY SMALL part in the feel issue. Slimy feel is really affected by water pH, carbonate content, sodium content and of course the type of soap being used.
Soft water (for most applications) is water that contains less than 1 Grain per Gallon (GPG) of Calcium Carbonate hardness.
Hard water contains calcium and magnesium ions. When you use soap (real soap, not a Synthetic detergent/surfactant) in hard water, the soap will react dramatically with the hardness to create that rough sticky precipitate known as soap scum or soap curd. Soap curd sticks to everything that it touches…skin, hair, clothing, bathtubs, shower curtains, shower stalls etc… it is a general nuisance and visual evidence of hard water’s inability to clean properly.
When you use real soap with soft water, there are no ions to react with the soap and it lathers quite spectacularly. The lather is evidence of preserved cleaning power. That is why softener salesmen can make claims like “whiter whites, brighter brights, and darker dark’s” – it’s actually true.
Of course, there are different kinds of SOFT water…
- Naturally soft water – Water that is naturally devoid of hardness ions. Rainwater is usually a good example of this
- Ion exchange softened water – Water that has been processed using ion exchange to replace hardness ions with sodium or potassium.
- Chemically softened water – Hardness ions ore sequestered chemically by chelating agents like Sodium Tripolyphosphate (STPP) – Do you remember Calgon ?
- Purified Water – Water “purified” through a distiller, reverse osmosis nanofilter, electrodeionization(EDI), or CDI array. – the hardness ions are physically removed, but not replaced with anything else.
This is where things scan get confusing, since these types of soft water react DIFFERENTLY with soap.
- Sodium Ion exchange softened water will feel slimy with most soaps, since they are made from lye
- Sodium Ion exchange softened water will not feel slimy with potassium-based soaps like Dr Bronner’s Potassium Hydroxide liquid soaps.
- Chemically softened water will usually feel slimy
- Naturally Soft water rarely ever feels slimy with sodium or potassium-based soaps
- Purified water rarely ever feels slimy with sodium or potassium-based soaps
- If you use a high pH soap, it will feel slimier than a low pH soap.
Regardless of the amount of hardness in the water:
- Low pH soft water will feel rough, no matter what.
- Low pH is bad since it neutralizes itself by corroding pipes, fittings, fixtures and appliances.
- High pH soft water will generally feel slick/slimy. (Try adding varying amounts of baking soda to a bowl and washing your hands in it).
- If your soap has high levels of oleic moisturizers, then you can even get a “greasy” feel if the pH and sodium levels are high enough.
- Carbonate Alkalinity will change the feel of the water, as well the effectiveness of various cleaning products.
Here is a list of different soaps and their average pH
Irish Spring 9.5
Lever 2000 9.0
So when you’re looking for more or less slime, consider the above and enjoy your clean water!