Hard water has a high mineral content.
Levels:
0 to 60 mg/L Soft water
60 to 120 mg/L Moderately hard water
120 to 180 mg/L Hard water
180 mg/L or higher Very hard water
Link to the calculater for your area:
www.kinetico.co.uk/hard-and-soft-water-explained/hard-and-soft-water-uk
(Scroll down and enter your postcode in the box).
Hard water can affect the skin on your scalp causing dryness and itching. It may feel like it does when you haven't thoroughly rinsed out all of your shampoo.
Soft water is better at penetrating the hair shaft than hard water. This means that hair washed in soft water tends to be shinier and softer as the water helps the hair shaft to remold itself properly. In contrast, hard water can be drying to the hair, making it appear dull and potentially more brittle as the shafts cannot remold in the same way, leaving them with a rougher exterior.
Hard water also reduces voulme, removes colour from the hair quickly and can mean that products aren't washed away from the skin properly (leading to dryness and irritation).