Investigations have been made of the effect of diffraction on the propagation of acoustic impulses in water. Gaussian shape pressure pulses were obtained by applying 0.2‐μs‐wide voltage pulses to thick piezoelectric plates that act as piston sources. Acoustic probe techniques were used to examine in detail the resulting pressure profiles. These are strongly affected by diffraction phenomena, and because of the transient nature of the process, special care must be taken in interpreting the observed data. Comparisons between experimental and theoretical time and space pressure profiles are presented.