The basic difference between hard and soft water is that hard water reacts with soap to form solid soap scum and soft water does not form soap scum. The formation of soap scum on your skin is the reason that soap seems easier to rinse from your body.
A general scale would look something like:
- 0-50 ppm is considered soft water
- 51-110 ppm is considered medium hard water
- 111-200 ppm is considered hard water
- 200 ppm is considered very hard water