Standard Plate Count Test (SPT):
The bacteria are made to grow as colonies by inoculating a known volume of water sample in a solidifiable nutrient medium (Nutrient Agar). The water sample is kept in a petridish and nutrient medium poured on the petridish. The petridish is kept for incubation at 35oC for 24 hours. The colonies of bacteria, if present, develop as spots and are counted down. The bacteria density is expressed as number of colonies for 100 ml of sample. If more colonies develop, counting becomes difficult. In that case, the sample is diluted with sterile water and SPT done and the dilution factor is accounted while expressing the result.