The only waste that is routinely dumped is from the galley drains or possibly lavatory sink drains . In flight, water from these drains evaporates long before hitting the ground.
I don't really know where you are going with this question but I might as well bring it up... human effluent (blue water) is stored in tanks and disposed by service trucks (for lack of a better term "turd hearse") upon arrival at your destination. Sorry for the bathroom humor.
If your question comes from noticing fluid draining from an aircraft as you boarded, the source was probably condensation draining from the airconditioning system or water waste from a galley drain. The company for which I work has a policy that flight attendants may not dispose of liquid while at the gate. Ramp personnel generally do not enjoy being dowsed by hot coffee.