Is the free water along the canals in Wales drinkable?
Technically, maybe. Advisable, no.
The water comes from outdoor spigots to which you attach your boat's rubber or plastic hose. Presumably, the water is from safe wells or municipal water systems, but Europeans drink bottled water for a reason. Actually, two reasons: often the water ISN'T safe due to arsenic, which often occurs naturally in well water, or other toxic substances such as lead from old pipe joints; and, public water often simply tastes bad, especially in big cities like London, Paris or Rome.
The water goes from the hose into a large tank on the boat -- and who knows how clean it is? On our canal boat vacation, we showered and washed dishes with the boat's water supply, but we drank bottled water.