I’ve had water hardness quoted to me in ppm and degrees Clarke and also in grains – I’m very confused?
We’re not surprised. Milligrams per litre (mg/l) and parts per million (ppm) are the same scale of measurement. In other words 300ppm is the same as 300mg/l. Degrees Clark (°Clark) was commonly quoted in the UK many years ago but is little used today. 1° Clark is equivalent to 14.3ppm or mg/l. It corresponds to one grain of calcium carbonate in one Imperial gallon of water or 14.3 parts of calcium carbonate in 1,000,000 parts of water. It is unusual to have hardness referred to in grains per gallon (gpg). This is a term commonly used in America and associated with the US gallon. I gpg is equivalent to 17.1mg/l. There are also French and German degrees which can confuse matters even further so we won’t go there.
