Hydro-1-15 Color Change Developer (12oz Aerosol) (part 1 of a two part system) Color Change Detector for Cold Water Leaks in a Humid Atmosphere: a 2-part system Hydro-1 is a color change developer sprayed on the outside of a potential leak site. Hydro-2 is a liquid tracer which goes into solution with the test water. Hydro-2 causes a visible color change from orange to purple when it comes in contact with the Hydro-1 developer. Use for testing of large tanks, vessels, complex piping systems, flexible containers and systems that inherently contain or will contain water. It can also detect leaks in valves, fittings and welds. It is formulated to prevent false indications due to high moisture in the air or cold piping that can condense water on its surface. Taking photographs of the test results makes work easy to substantiate.