Water largely isn't fundamenally transformed with use (unless it's involved in a chemical reaction, though that's a minute fraction of all water usage), though it may be dispersed or degraded (usually contaminated with something). But it can recover its earlier state with appropriate applications of process and energy. Water (and much else we consume) is a material input rather than an energy input.
With energy inputs it is the energy potential itself which provides value, and that potential is intrinsically consumed in their use. Water, wood, iron, aluminium, lithium, helium, etc., can all be recycled, restored to their useful state, at comparatively little cost.
Collecting the waste products of food don't give you that, on two counts. First, most of the actual metabolic output is gaseous and lost to the atmosphere at large (CO2 and water vapour in your breath), and to the extent that solid and liquid human waste are useful in producing new food, it's a nutrient fertilisers which enable energy conversion of sunlight to fuel, and not the primary energy input itself (sunlight).
