hmm, now if ur really resourceful, bring an empty milk gallon jug on board, and fill it up in the sink... and use that as extra water...i'm sure the sink will have hot water. Also bring in a cup to fill the jug...

the shower time is a bit short, u got to factor in the weight of the water that stays on the plane the whole flight, 5 minutes = 5 gallons = 40 pounds or so. 10 pax = 400 pounds of water = extra fuel consumed. Maybe if they let you purchase blocks of water beforehand? or is it limited by the tank...what if ur the only F pax? then can you get 50 minutes or do they just fill the tank up based on what they need?