Add tablets to a water sample; use 2 tablets in 50ml or 1 tablet in 10ml and shake to dissolve. The resulting colour change will indicate whether the ward is hard or soft.
Green indicates that the water is soft.
Red indicates that the water is hard.
The colour change takes place at 20mg/l hardness as CaCO2 on a 10ml sample. Range 4, 8, 20mg/l