An ergonomically optimized, in-line water valve assembly for use with a dental handpiece comprises a body having a plurality of channels to accommodate the flow of water and/or air to drive and cool the dental handpiece. A portion of one such channel, the channel that supports the flow of coolant water to the dental handpiece, comprises a resilient collapsible tube. The water valve assembly further comprises an actuation screw that, when rotated in a first direction, drives down upon and collapses the resilient collapsible tube, thereby enabling an operator of the water valve assembly to disable or decrease the flow rate of coolant water to the dental handpiece. Rotating the actuation screw in the opposite direction enables the operator to enable or increase the flow rate of coolant water to the dental handpiece.
