refer to standard Methods for Examination of Water and Wastewaterhttps://www.standardmethods.org/store/

You can go for MPN. Plating and semiquantitative counting can be done.

this is the classic R2A medium http://aem.asm.org/content/49/1/1.full.pdf

use serial dilution of your sample and then do the pour plate! pour plate should be done with 5 or more plates for each dilution. count the average and CFU per ml. in this method even anaerobic bacteria have a chance to grow.

Serial dilution is the simplest way to determine the bacterial count.