The invention provides for the use of at least one aromatic acid compound of formula i), or a salt thereof, as a water tracer; wherein n is 0, 1 or 2, R1 to R5 are each independently H, alkyl or alkoxy and wherein at least one of R1 to R5 is alkoxy. The invention further provides for a method of monitoring the flow of water within a structure having an inflow point and an outflow point, where the method comprises; a) introducing at least a one tracer of formula i) into said inflow point; b) collecting fluid at said outflow point; and c) measuring the presence and/or concentration of said tracer in said fluid collected at said outflow point over time
