Distilled water is not supposed to contain > 5μg of chlorides and if it does, distillation is unsuccessful, and a repeat is needed. The quantification of chlorides post purification of reagent grade water though serves to illustrate the success of purification, has also been used in this study to illustrate nearness to success. A total of 50 registered Clinical Chemistry Laboratories in Lagos Mainland of Lagos Nigeria were recruited in this cross sectional study, their reagent grade water sampled and tested for chlorides using spectrophotometric technique. A questionnaire was also administered to ascertain the Laboratories’ source of water. In this study, significant amount of chloride was detected in all reagent water tested with concentration range of 0.055mg/L - 38.760mg/L. Most laboratories studied had Borehole as their source of water with few using bottled table water. The concentration of chlorides in laboratories using bottled table water ranged from 0.142 to 4.70. The average chloride concentration was 1.560mg/L and Variance of 2.953. This when compared to borehole sources with average chloride concentration of 5.912mg/L and variance of 79.378, at 95% confidence interval, p = 0.05, critical value 2.021 and calculated t = 2.896, was statistically significant. There is detection of significant concentrations of chloride implying failure of purification of water in all Laboratories studied. However, based on this study use of bottled table water is presently better than use of borehole as source of water for purification.