Which type of testing uses liquid to check for leaks in sewers?

The type of testing that uses liquid to check for leaks in sewers is dye testing. This method involves introducing a colored dye into the sewer system, which can help identify leaks by tracing the flow of the dye to surrounding areas, such as surface water or groundwater. The visual presence of the dye outside of the intended sewer path indicates a leak or an issue within the system, making it an effective method for leak detection.

Other methods, like smoke testing, involve introducing smoke into the sewer system to identify leaks or problem areas, but they do not use liquid. Air testing uses air pressure to detect leaks, but again, it does not involve any liquids. Hydraulic testing evaluates the stability and efficiency of a sewer by monitoring the performance under a specific load of liquid, but it is primarily focused on system performance, rather than direct leak detection. Dye testing remains the most suitable choice for specifically checking for leaks in sewer systems through the use of a liquid medium.