an installation for connection to a water piping system comprising a water main and at least one branch pipe , for preventing a stagnation of water inside that branch pipe . a pumping unit is connected to first and second openings in the far end of the branch pipe for pumping water samples out of the branch pipe through the first opening , and back into the branch pipe through the second opening . the installation also comprises a conduit extending inside the branch pipe from the second opening to a proximity of the water main . the pumping unit is continually or intermittently operated for sampling a portion of the still or slow moving water at the far end of a branch pipe , and for pumping these water samples near the water main where the water flow inside the pipe is more active . such circulation of water in a branch pipe prevents the stagnation of water at the far end of the branch pipe . in another aspect , there is provided a method for preventing stagnation of water in a water supply system . the method comprises the steps of extracting water samples from the far end of the branch pipe relative to the water main and pumping the water samples into the near end of the branch pipe through a branch valve and toward the water main .