Last time I walked the VDLP was in 2018, but I do remember finding a serious lack of potable water from fountains etc, Much of the Plata is low lying, and so agricultural runoff and contamination is an issue and not many fast rivers, until you are further north.
But bars and restaurants where you stop for breakfast or coffee will fill bottles for you. With many towns and villages far apart, take plenty with you and refill at every opportunity, especially in the warmer months if you are crazy enough to walk it then!