Heavy metals are chemical elements with a specific gravity that is at least 5 times the specific gravity of water. The elements studied were mercury, lead, arsenic, cadmium and chromium. Heavy metals have no useful biological function in the body but might be highly toxic as they cause precipitation of proteins especially the enzymes. This investigation was therefore carried out to estimate concentration of these metals and their influence on biological system. For this purpose drinking water samples were collected in one litre polyethylene bottles adding 5 mL of concentrated HNO3 as preservative to adjust the PH<2.00 to maintain heavy metal concentrations during analysis. Samples were marked with unique numbers with dates for the study of Acid Extractable metals. Similarly samples were prepared and preserved for micro biological testing.

The metallic ions were estimated by Atomic absorption spectrophotometer of Perking Elmer Model A. Analyst; 2003 at recommended wavelengths for metal ion. Acetylene gas was used as fuel (at 8 psi) and air as an oxidizer.

Statistical analysis was done. The calibration curves were prepared separately for all the metals by running suitable concentrations of the standard solutions. It was evident that concentration of chromium, lead, mercury, arsenic and cadmium were high in several drinking water sources in Lahore. This problem is particularly alarming for ground water sources. Almost all water sources are contaminated with lead. According to WHO maximum acceptable limit 10 ppb ,8 water sources had mean chromium concentration in water samples above maximum acceptable limit of WHO (50 ppb), 94 water samples were contaminated with cadmium according to WHO maximum acceptable limit (10 ppb), 13 water sources had arsenic concentration above maximum acceptable limit according to WHO (50 ppb) where as 7 water samples were having concentration of arsenic less than minimum acceptable limit according to WHO (10 ppb) and only 5 water sources meet the criteria of WHO for concentration of mercury, the acceptable limit of 2 ppb.

Multitube Fermentation Technique/MPN Method as described by Mackie & McCartney was used for microbiological analysis i.e. Colifcrm bacteria. The results of this study revealed that both samples i.e. tap and ground water do not show conformity with the standards for safe portable water recommended by WHO. The most frequently encountered pathogen in this study was Escherichia Coli which was isolated more in ground water than tap water.

It is therefore concluded that by using Atomic Absorption Spectrophotometer concentration of heavy metals in water can be determined and thus on the bases of this work precautionary measures can be taken to prevent the health hazards of these toxic metals. Similarly microbiological analysis of drinking water has provided the evidence that most of the water sources are contaminated with microbes.