A hydro-testing is a process in which pressure vessels such as pipelines, plumbing, gas cylinders, boilers and fuel tanks can be tested for strength and leaks. The test involves filling the vessel or pipe system with a liquid, usually water, which may be dyed to aid in visual leak detection, and pressureization of the vessel to the specified test pressure. Pressure tightness can be tested by shutting
off the supply valve and observing whether there is a pressure loss. The location of a leak can be visually identified more easily if the water contains a colorant.