The present invention provides a method and related apparatus for determining the rate of flow of a liquid, the liquid comprising a first liquid delivered to a point (24) with at least a second liquid to form a solution of the first and at least second liquids, the method comprising the steps of determining the rate of flow of the at least second liquid, delivering the solution to a conductivity-measuring means (38) by which the conductivity of the solution is measured, determining the ratio between the first and the at least second liquids in the solution on the basis of the conductivity of the solution and determining the rate of flow of the first liquid on the basis of the rate of flow of the at least second liquid and said ratio and wherein the rate of flow can be employed in calibrating a flow controller controlling the rate of flow of the first liquid.