I assume you mean which gives least lather with solid soap. It will be the hardest water, that is the one with the most calcium and/or magnesium compounds.
Hard water tends to produce less lather compared to soft water. This is because hard water contains minerals like calcium and magnesium which can react with soap, forming insoluble compounds that reduce lather formation. Soft water, on the other hand, does not contain these minerals and allows soap to lather more easily.
hard water
Shampoos produce lather due to the presence of surfactants, which are chemicals that reduce the surface tension of water. When mixed with water, surfactants trap air to form bubbles, creating lather as the shampoo is massaged into the hair. The lather helps to distribute the shampoo evenly and cleanse the hair effectively.
Soft water produces more lather when soap is added compared to hard water. Soft water has fewer minerals, such as calcium and magnesium, which can react with soap to form a scum that reduces lather production.
lather
Lather would be the combination of two, middle ground or in bathing it is the soapy, bubble mixture of shampoo and water.
Water is a universal solvent and there are two types of water i.e hard water and soft water. Soft water is the water that easily lather with soap while hard water does not lather with soap and is also of two type i.e temporary and permanent.
There are a few reasons why your shampoo may not lather as expected. One common reason is using too much shampoo or having hard water, which can reduce lather. Additionally, certain hair products or natural oils on your scalp can also affect lather. It's important to follow the recommended usage instructions and consider factors like water quality and hair products when troubleshooting lather issues.
In soap titration method, lather refers to the frothy soap solution produced when soap is agitated with water. This lather is used to determine the endpoint of the titration process by observing changes in its appearance or behavior. The amount of lather formed can indicate the amount of soap present in the solution.
Soap lather helps to lift dirt and oil from the skin, allowing it to be easily rinsed away. It is created by mixing soap with water and agitating the mixture to incorporate air bubbles, which create the frothy lather. The lather helps to distribute the soap evenly and enhance its cleansing properties.
Soapy water is a solution of water mixed with soap or detergent. When it becomes frothy but does not produce a lather, it usually means that the solution has trapped air bubbles within the liquid, creating a frothy texture.
Sodium palmitate produce a permanent lather with hard water..