The process of particle bed contact flocculation and filtration was investigated. A solution to the filtration equations was presented and a new theory describing the flocculation of the primary particles inside beds of granular media was established. The flow root mean square of velocity gradient inside granular media beds as well as the bed head loss were presented in new different models as functions of both bed depth and time of filtration. Experimental verifications of the developed models were provided using the data collected by other investigators as well as the writer's own data. The applications of the filtration theory to the design of granular media filters and pilot plant studies were discussed and solved examples were presented. A new method for conversions of turbidity data in FTU or mg/l units to volume of deposits per bed volume was also included.