Methods of analyzing low levels of peroxyacetic acid (PAA) in water are described. These methods employ buffering the PAA-containing water and the use of a N,N-diethyl-p-phenylenediamine (DPD) indicator system in the presence of iodide ion. The intensity of the pink coloration that develops is quantitated by colorimetric or titrimetric methods and correlated to the ppm PAA in the water. Positive interference effects due to the presence of hydrogen peroxide are eliminated by performing the analyses quickly after the introduction of the reagents.