The Oatey Leak Detector Blue is a dye used to find leaks in plumbing and HVAC systems. It contains a blue fluorescent dye that glows yellow-green under UV light to pinpoint leaks. Suitable for PVC, CPVC, ABS, and metal piping, it is safe for potable water systems and won't stain fixtures or pipes. The concentrated dye requires only a small amount; a 4 oz bottle treats up to 25 gallons. It meets NSF/ANSI Standard 60 for drinking water systems, providing an effective way to detect leaks before major damage occurs.