In this research, the positioning control of a water hydraulic servo cylinder system with the simple adaptive control (SAC) is discussed. Conventional model reference adaptive control (MRAC) also achieves good tracking performance for cylinder control, but the controller structure is much more complicated and has less robustness for disturbance in real application. Compared with MRAC, SAC has simpler and lower order structure, i.e. higher feasibility. In this paper, we examined and evaluated the control performance of SAC on a water hydraulic servo cylinder system. With the recent increased concerns over global environmental problems, the water hydraulic technique using pure tap water as a pressure medium has become a new drive source comparable to electric, oil hydraulic and pneumatic drive systems. This technique is also preferred due to its high power density, high safety against fire hazard in production plants, and easy availability. However, the main problems for precise control in a water hydraulic system are steady state errors and overshoot due to its large friction torque and considerable leakage flow. To compensate these effects, MRAC had been already applied and the better control performances were obtained. However, no result has been reported on SAC application for water hydraulics. To make clear the merits of SAC, tracking control performance and robustness were discussed via experimental results. It was confirmed that SAC gives 1) better tracking performance compared with PI control, and 2) comparable control precision with MRAC within 70 micrometers to the reference position and higher robustness for parameter change despite simple controller. These results ensure wider application of simple adaptive control in real mechanical system.