I once made a cooling system for a small server room that used tap water.
I don't want to recommend this though, because running significant amounts of water through a server room is generally a bad idea
I got some aluminium sheet bent to a duct shape, so that it ran from about 20 cm from the ceiling to about 50 cm above the floor. Inside the duct i placed several of the larger type radiators that are used when cooling overclocked computers with water. At the end of the duct I placed 3 20mm fans that would pull air through from the ceiling down through the radiators and out at the bottom. A thermostat stopped the fans and waterflow (magnetic valve) when the temperature was low enough. Radiators were connected in serial, so that the coolest water was closest to the fans.
This server room was inside an industrial area where water was abundant and free of charge, so water came right from the pipes, ran through the radiators in the duct, and then right down the drain after cooling the air.
CONS: Not a very efficient setup, requires some DIY work, and you risk flooding your server room.
PROS: In this case it was cheap, and we had no accidents
Pound for pound, the amoeba is the most vicious animal on earth.