Abstract: An apparatus for measuring characteristics of a liquid including a channel through which, during operation, the liquid flows and a plurality of sensors for measuring characteristics of the liquid as it flows through the channel. The cross-sectional shape of the channel varies along its length, but the cross-sectional area of the channel is substantially constant so that, during operation, liquid flows through the channel at a substantially uniform speed. The sensors include an ultra-violet sensor and an infra-red sensor, each having a source and a detector of electromagnetic radiation arranged along an axis transverse to the channel. The axes of the two sensors are transverse to each other.