Abstract. The aim of the study was to investigate and assess the quality of drinking water, obtained from own well source at a pig farm (with an average daily number of reared pigs 532 units), situated in South Bulgaria, Plovdiv Municipality, on the base of main organoleptic, physical, chemical and microbiological indices. For this purpose once a month (from July 2009 to March 2010.) water samples were collected and analyzed by reference methods of Bulgarian State Standard. It was found that the quality of water correspond to the norms concerning organoleptic indices (smell – State 0, norm up to State 2; color – 5°color degrees, norm up to 15°color degrees; visibility – over 65 cm thickness of the water plast through that should clearly seen special text, norm at least 30 cm; taste – no flavor, norm no flavor), chemical indices (pH 7.45÷7.75, norm 6.5–9.5; oxidizability 0.72÷2.16 mg O /L, norm up to 5.0 mg O /L; total hardness 2.82÷4.45 2 2 mg Σqv/L, norm up to 12.0 mg Σqv/L; content of chlorides 20.3÷36.0 mg/l, norm up to 250.0 mg/L, ammonia – not proved, norm up to 0.50 mg/L, nitrites 0.007- 0.094 mg/L, norm up to 0.50 mg/L, and nitrates 3.0÷25.0 mg/L, norm up to 50.0 mg/L) and total number of cultivable microorganisms (5 -18 CFU/mL), norm – without significant variability of the index value of the investigated water. The only exception was found for the water temperature, whose maximum values exceeded the requirements of the standard (16 oC) and number of Escherichia coli (Coliform’s test), which values were higher than norm (0 CFU/100 mL), for both indices during five months from the studied period. The deviation in the quality of water in respect content of E. coli suggests anthropogenic pollution on groundwater of the own well with coliform bacteria, containing in manure and urine from the pigs in the farm. Organoleptic, chemical and microbiological characteristics of the sampled water meet the requirements of the Dutch standard for drinking water for pigs. This standard allows higher level of oxygenation of the water and higher levels of ammonium and nitrate content in water compared to Bulgarian standard for humans and animals drinking water. Perhaps time has come, as in the Netherlands to develop a national standard for drinking water, which be applied only to farm animals.