A dripper defines a fault in an underground sewer where water is slowly ingressing into the sewer in small drips as opposed to seeping continuously. Defects in underground piping can occur in the form of cracks, perforations or breakages. Ground water can then drip into the sewer adding water loading to downstream processing activities.
Trenchlesspedia Explains Dripper
Many cities have ageing underground sewer systems with piping networks made of inferior materials that are no longer in use (like clay). Over time ground subsidence or construction activities, or even the roots of trees can damage these pipes leading to small fissures or large breakages. A dripper is a failure, which only allows a small amount of water ingress to drip into the sewer. A combination of many small failures like this can have a cumulative effect of adding to the water flow of the sewer. A dripper is also likely to get worse in time leading to further water ingress and associated problems.