Roof Rack Water Tank | Carrying Water On Your Rig

For overlanders and campers, water is the heaviest thing you pack, and storing it inside eats cargo space. A roof rack water tank solves that by riding on top, using a mounting system that straps or bolts the tank to your crossbars. Whether a roof rack water tank works for you comes down to your rack’s load rating, your vehicle’s roof strength, and the tank’s mounting hardware.

What Is A Roof Rack Water Tank?

A roof rack water tank is an exterior water storage container built to mount on roof racks, crossbars, roll bars, trunks, and similar flat surfaces. Unlike a portable jerry can you strap down, these tanks use a dedicated mounting system with backing plates and bolts to hold them in place. They connect to a hose or spigot for washing gear, showering, or filling a camp sink.

Current retail examples show the range:

• Dometic Pro Water Tank With Mounting System / 20L: 20L / 5.2 gal capacity, a popular roof-mounted option with an integrated pump and shower kit available separately.
• Pak Offroad RAKTANK (Part # RTFKUNI5): an 8 gal / 30L universal-fit tank with a five-point backing plate system for a secure flat mount.

Most tanks use aluminum construction for a balance of weight and durability.

How To Mount A Roof Rack Water Tank

The most defensible mounting procedure comes from the Pak Offroad installation guide, which spells out exact steps and torque specs. Here is the correct order for a secure flat installation:

1. Confirm your rack is compatible. The tank must mount completely flat on the surface, and the rack or crossbars must be approved for your specific vehicle.
2. Install the mounting pins for traction boards if your model includes them.
3. Place the tank on the roof rack and position all 5 backing plates underneath the rack surface.
4. Align the bolts through the T-slot, making sure each bolt sits central to the baffle hole and never touches the tank body.
6. Let it sit, then re-check torque. The guide says to allow the assembly to settle and verify tension over the bolts again before finishing.

The last step matters more than it looks. Nyloc nuts and backing plates bed in after a few minutes of vibration, and a loose bolt on a 92 lbs tank is how racks fail mid-drive. If you’re comparing models before buying, our tested roundup covers the best roof rack water tank options on the market with real-world fitment notes.

Critical Safety Rules For A Full Tank

Skipping the safety constraints turns a useful accessory into a roof-load hazard. The Pak Offroad documentation warns that the mounting surface must be strong enough to retain the mass of the fully loaded tank, and every backing plate must be used. The biggest mistake is treating the tank like cargo — it’s not strapped down, it’s bolted on, and the hardware has to carry the load.

The other non-negotiable rule: bolts must never touch the tank body. The guide is explicit on this point, because a bolt rubbing against aluminum creates a puncture risk that will leak water down your roof and, worse, compromise the tank’s structure mid-trip. Check clearance before you torque.

Here’s the honest math on weight:

Before buying, check two numbers: your rack’s dynamic load rating (while driving) and your vehicle’s roof load limit from the owner’s manual. Also mount the tank horizontally — a vertical or tilted install increases water sloshing, which shifts the center of gravity mid-corner.

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