Water plays an important roll in the epidemiology of a lot of infectious diseases. Groundwater as well as surface water contains generally microorganisms of several species, which cannot always differentiated properly in autochthonous flora and contaminants with health significance. Sources of bacterial or viral contaminants may be feces from man and/or animals but with different counts in ground and surface water. With respect to water used for supplying farm animals it is stated that it must have initially drinking water quality. Since it generally looses this quality in this supply system the following requirements shall be met: Free of Salmonellas and/or Campylobacter in 100 ml, no E. coli in 10 ml, total bacterial count at 37 degrees C less than 1000 cfu/ml and total bacterial count at 20 degrees C less than 10,000 cfu/ml.