Hydrogen peroxide ($H_2O_2$) plays an important role in natural water samples. In this study $H_2O_2$ concentrations were quantified in different water samples by chemiluminescence detection. This method was chosen because of its high sensitivity and suitability for determining low concentrations of $H_2O_2$. $H_2O_2$ is introduced to the oxidation reaction of alkaline luminol solutions in the presence of $Co^2+$ ion catalyst. When these components are mixed, blue light ($lambda$ = 440 nm) is emitted. Maximum chemiluminescence intensity occurs within 2 s after mixing and is continuous for up to a few minutes, permitting accurate measurements at selected delay times. $H_2O_2$ concentrations being very low in water samples made us use the standard addition method. Thus the sample luminescences were measured by the addition of 25 $mu$ L 0.075 M $H_2O_2$ standard solutions. The $H_2O_2$ content of water samples was between 0.13 mM (in snow water) and 1.51 mM (in Gölbaşı Lake water). The results indicated that $H_2O_2$ concentrations in surface waters are representative of aquatic life.