Backflow

n. flow that moves in the opposite direction of what is desired or usual

Noun
1. a flow that returns toward its source
(synonym) backflowing
(hypernym) flow, flowing
(hyponym) regurgitation

A reverse flow condition created by a difference in water pressures that causes water to flow back into the distribution pipes of a drinking water supply from any source other than the intended one.

Synonyms and related words:
Charybdis, Maelstrom, back stream, backwash, backwater, countercurrent, counterflow, counterflux, eddy, gulf, gurge, maelstrom, refluence, reflux, regurgitation, swirl, twirl, vortex, whirl, whirlpool