You considered one source of power: gravity on water. What sources of power might you have available? Electricity? Compressed air? How about gravity on a movable weight? Use the moment created by a weight on a lever and fulcrum. The farther the weight is from the fulcrum, the greater the moment imposed on the other arm. The weight could be supported by rollers on a horizontal arm extending from a fulcrum (pivot) point. The opposing arm of the lever is vertical and resisted by the player. So, the player is supporting the weight by pushing horizontally. The machine operator moves the weight away from the pivot point thus increasing the force the player resists.