Among the numerous detection methods applicable in spectroscopic gas detection systems photoacoustics is probably the simplest, most cost effective, yet a highly sensitive one. By using a properly designed photoacoustic cell, equipped with a commercial microphone and electronics for phase sensitive detection, absorbed electromagnetic radiation as low as 10 nW can be easily detected. The choice of a suitable light source for PA gas detection, however, is crucial in order to preserve the simplicity and practical advantages of the combined gas detection system. In the photoacoustic system presented here, therefore, external cavity diode lasers have been adopted. Contrary to ordinary diode lasers, external cavity diode lasers are ideal sources for spectroscopic studies as they have a narrow linewidth and ar continuously tunable in a relative wide wavelength range. External cavity diode lasers operating in different wavelength range have been developed and concentration determination of water vapor gaseous mixtures are presented. Sensitivity of the system presented here could reach the ppb. level under optimal conditions.