Abstract: A method of digital assessment of chemical dip tests is disclosed. A photograph of a dip tester including a colour change pad is taken with a mobile device, for example a mobile phone. The dip tester is photographed on or alongside a reference card, with both the dip tester and the reference card in the same frame. A processor on the mobile device analyses the photograph thus obtained to determine a value for a characteristic of water being tested. The characteristic may be for example, pH, concentration of iron, concentration of copper. The water may be central heating system water.