• (n.) An instrument for determining and recording the quantity of water discharged from a pipe, orifice, etc., in a given time.
Hy`dro·met'ro·graph noun [ Hydro- , 1 + Greek ... measure + -graph .] An instrument for determining and recording the quantity of water discharged from a pipe, orifice, etc., in a given time. 
hydrometrograph An instrument that measures and records the rate of water discharge from a pipe or an orifice.