Abstract: The effect of phosphorus on the assimilable organic carbon (AOC) and the bacterial regrowth potential (BRP) in deionized water with necessary nutrients addition is studied.It is shown that phosphorus would become the limiting factor on bacterial regrowth when its concentration is low enough.At the same time,pilot-scale drinking water treatment processes are used to treat the raw water and the effect of phosphorus on the biological stability of the treated water was studied.It was shown that after 50μg/L PO₄^3--P was added to the treated water,the AOC of the treated water increased 55% and the BRP increased 123%.This indicated thatphosphorus was the limiting nutrient of bacterial regrowth in the treated water.Because the conventional drinking water treatment processes could effectively remove phosphorus from raw water,the results got in the experiment indicated the possibility and feasibility of ensuring the total phosphorus(TP) in drinking water less than 5 μg/L to restrict microbial regrowth in drinking water distribution system in China.