Cleaning method of a water-filtration system under operation

The present invention concerns a method for cleaning a filtration system under operation, said filtration system comprising: a hydraulic circuit Cp recycling the permeate stream to the feed side of said membrane and/or a hydraulic circuit Cr recycling the retentate stream to the feed side of said membrane, said method comprising: 1) injecting an amount of a chemical product into the filtration system which is under operation in said hydraulic circuit Cp or in said a hydraulic circuit Cr or upstream of said cross-flow filtration membrane, 2) setting the proportion of recycled permeate stream or recycled retentate stream collected in the hydraulic circuit Cp and/or Cr to enable the recycling of a significant amount of unreacted chemical product having passed through said cross-flow filtration membrane to the feed side of said cross-flow filtration membrane, as well as a filtration system for carrying out said method.