Used primarily in plumbing and HVAC system testing to visually detect leaks. The blue dye is added to water, making it easy to trace the path of water flow and identify leaks in pipes, valves, or connections. Commonly used during system commissioning, maintenance, or troubleshooting. The colorant is water-soluble and non-toxic at recommended concentrations, making it safe for use in potable water systems. Also used in drain inspections to confirm flow paths and detect cross-connections between fixtures.