Travelling with fresh water

The loss in MPG is so negligible that you cannot measure or quantify the loss.

In theory you will use more fuel how ever the amount is so small that you will not notice the difference at all.
I travel with my fresh tank full at all times.

Our TH carries 830# of fresh water. I've never noticed a difference in fuel consumption.

want better mpg slow down 5mph.

Our rig has a capacity for 80 gals of fresh water. We usually carry about 30. We always have a 30 gal plastic food safe container with us that allows us to get water and pump it into the RV, should we not be able to use the campground water or the spigots are too far away (at State campgrounds the latter is usually the case). I would never travel without some water for the reasons listed already. We also bring 4 or 5 gallons of water from out tap at home for drinking and cooking.

with us it all depends on the final destination and whether there is water there or not. some times when we boondock we fill up at our last gas station. they have a real nice water faucet just past the pumps and they have told us to just carry enough water over the mountain passes for potty breaks and fill up with water free any time we come in. real nice people to know if I say so. If you don't have that convenience, then carry your water with you. it is a must have in that case.

You won't notice an mpg difference.

Please keep in mind the weight of water, and the location of your tank. If it's forward of the wheels it will add quite a lot to the tongue weight. If it's aft of the wheels it will remove quite a lot of weight from the tongue, which could be dangerous.

In either case you'll likely need to compensate by changing where you put other stuff and adjusting your WD.

Sometimes other folks water just plain sucks.. Bring your own fixes that. I'm always full for the things that can and do happen.

Be prepared for the boiling order.:B

38 years RV'n ALWAYS with a full tank.

Broke down over a weekend, guess what, yep a full tank of water.

Always, Always have an empty black tank. I know this for a fact. You will too if you ever have to use a 5 gallon bucket to manually drain enough to use it. Folks at the repair shop were great about this. dumped it in their restroom.

Always travel, Full and Empty, Empty. Ya never know.

I haven't noticed any difference that would cause me to stop bringing water. Our rig can carry over 100 gallons across 2 tanks and at the very minimum we carry at least one tank full which is over 400lbs. Our truck was properly sized to easily handle our rig's GVWR, we can't tell the difference towing when loaded with water. We have run into questionable water at some campgrounds so we prefer to bring our own (city water) from home, we rarely even connect to campground water and just run from the pump.

Overall weight is not as big a factor......wind drag is.
Face it RVs are not the most aerodynamic rigs.

We always travel with fresh water. Potty stops along the way, lunch etc.
Plus we got caught ONCE when CG water system had problems.