Table 2. Results of MPN and PCR microbial tests on samples taken from different parts of drinking water production and distribution networks of Arak city in the winter of 2011.

Methods	Quantity	MPN		PCR
		Positive	Negative	Positive	Negative
Samples of city water distribution network	36	0	36	5	31
Wells that supply drinking water to the city of Arak	41	0	41	0	41
Control samples	24	Positive control samples: 12
		Negative control samples: 12

PCR: Polymerase chain reaction; MPN: Most probable number of coliform.