hydrorheostat

hy·dro·rhe·o·stat

(hī'drō-rē'ō-stat),
A rheostat in which resistance to the flow of electric current is provided by water.

hydrorheostat

(hī″drō-rē′ŏ-stat″) [ hydro- + rheostat]
A device formerly used to control the flow of electric current by changes in water resistance.