As long as we're on the subject of running water, here's how I do it in my Jeeps...
I use 2-gallon Rotopax water containers for my water supply. The "active" one mounts either on the side of the Trail Kitchen housing:
Or, if I've got the kitchen drawer unit installed, on the front of the drawer unit, just behind the back seat:
The pump is mounted on the front of the Trail Kitchen:
In cases when I want a water supply/pump but don't need the full Trail Kitchen installed, the pump mounts under the kitchen battery; it's behind the aluminum plate on the Molle panel.
I actually have several pumps left over from when I was designing the Trail Kitchen sink option so the one behind the Molle panel can stay there all the time.
The pump is a demand pump, which means that it has a pressure switch that turns on the pump when low pressure is detected (when the faucet is opened) and turns off the pump when pressure builds up (when the faucet is closed).
The output of the pump is routed to the sink:
The pump plugs into the Trail Kitchen power panel; when the pump won't be in use I pull the plug.
When I don't have the Trail Kitchen installed, I've got a separate power panel that hangs on the battery cover that the pump can plug into.
A two-gallon Rotopax is a good amount of water but for a longer trip more is needed. There are lots of places to carry Rotopax.
The MORryde Overhead/Swing Down Molle Panel can hold two 2-gallon Rotopax or one 4-gallon (only one 2-gallon is installed in this photo):
There are lots of other places to carry Rotopax on a Jeep - on the tailgate hinges, on the spare tire, on the door hinges, on the MORryde JK side mount, on a roof rack... point being, you can carry plenty of water in 2-gallon Rotopax containers because there are so many places to carry them. Also, an empty Rotopax makes a good "gray water" container if the drain water can't be drained onto the ground off to the side of the campsite. As a Rotopax gets emptied, it becomes the next gray water container.
When you consider that a 6-gallon water tank is about the largest that will fit under a later model JKU, carrying 3 (or more) 2-gallon Rotopax doesn't sound like a bad idea.
One other thing about portable containers like Rotopax is that you can carry them to the water source rather than driving the Jeep to the water source.
I don't mean to sound like I'm against on-board water tanks, but portable containers seem to work pretty well for me.