sorry to burst your bubble,,but its not water that powers a fuel cell,
its hydrogen(H2) and oxygen(o2),,which then combine to produce
water,and energy.

To make hydrogen from water requires 36 kcal per mole - water being
one of the most stable compounds...which would require the building of
about 400 nuclear power plants just to electrolyze the water into
hydrogen and oxygen - to come even close to powering the US vehicle
fleet.