the drawing of external water into a water main as a result of a reduction in pressure in the water main (7)

single-celled organisms ranging in size from 0.5 to 5.0 µm (2)

the breaking down of complex substances into simpler substances by micro-organisms (11)

a water purifying powder mixture comprising a coagulant/flocculant and a disinfectant, available in Ethiopia (10)

a given amount of water for which there is a certain water tariff (13)