1) Those water pumps are durable. They service the water system in every RV and camper. I also had one on a boat for a hot water shower and it worked great. I think pressurizing the tank creates more problems than it solves.
2) The comments about "only 7 gallons" are off base. That is 10% of what I can run my entire RV on for 5-6 days including washing dishes, showers, general sink useage and flushing a toilet. Having that much water on hand to wash hands and general purpose is more than adequate for a couple days on the trail. I've had to use waterless hand cleaner many times and a half bottle of bottled water is more than enough to rinse your hands off.
Washing an entire jeep to make it mud free? No. But being able to spray off a muddy windshield or plastic side window would be great. More than once we've carried a 2.5 gallon jug of water for just that + emergency drinking water. (not that I would want to drink water stored in the bumper