Digital assessment of chemical dip tests

A method of digital assessment of chemical dip tests comprises providing a dip tester 10 and a colour reference card 12. A photograph of the colour dip tester is taken with a camera of a mobile device along with the reference card in the same frame. A processor identifies an area of the photograph corresponding to the colour change pad 14 of the dip tester 10 and an area of reference colours 18 on the reference card and determines the closest of the reference colours to the colour of the colour change pad of the dip tester. On that basis a value of a characteristic to be tested is determined, for example, pH, or concentration of iron, copper, or inhibitor. The water may be central heating system water or cooling water.