The Water Integrator was an early analog computer built in the Soviet Union in 1936. It functioned by careful manipulation of water through a room full of interconnected pipes and pumps. The water level in various chambers (with precision to fractions of a millimeter) represented stored numbers, and the rate of flow between them represented mathematical operations. This machine was capable of solving non-homogeneous differential equations.
Water analog computers were used in the Soviet Union until the 1980s for large-scale modelling.
References
Water integrator Wikipedia(Text) CC BY-SA