Water weighs about 8.34 lb per gallon
For planning, multiply gallons of water by about 8.34 lb per gallon. A 50-gallon fresh-water tank therefore adds about 417 lb when full. A 75-gallon tank adds about 626 lb.
Examples
30 gallons: about 250 lb. 50 gallons: about 417 lb. 75 gallons: about 626 lb. 100 gallons: about 834 lb.
That added weight matters against trailer cargo capacity and GVWR. Where the tank is located also matters because water position can change tongue or pin weight and axle loading.
Fresh water is not the only tank weight
Gray and black tanks also hold liquid. Their actual contents vary during a trip, so an RV can shift from carrying mostly fresh water at departure to carrying more waste-water weight later. Total vehicle weight can stay high even though the weight has moved between tanks.
Should you travel with a full fresh tank?
That depends on the trip and available capacity. If water is available at the destination, carrying less can reduce trailer weight. If boondocking or traveling where water is uncertain, the utility of a full tank may justify the extra weight. Either way, include the water in your loaded-weight calculation.
Watch cargo capacity
Water, propane, batteries, food, tools, camping equipment and personal cargo all add up. Use the trailer's actual ratings and, when possible, verify the loaded setup on a scale.
Frequently asked questions
How much does 50 gallons of water weigh?
About 417 lb using 8.34 lb per gallon.
Does RV water count against cargo capacity?
Yes. Water carried in the RV adds to the loaded vehicle or trailer weight and therefore uses available carrying capacity.
Can water change tongue weight?
Yes. The effect depends on tank location relative to the trailer axles and hitch, so filling or emptying tanks can change load distribution.