Building The Water Tank

Your water system can be as complex as you can imagine, with a rainwater catching system with carbon and UV light filtration (saw it on a bus conversion - no kidding) to carrying water in your cabinets in Jerry cans that you fill up at gas stations. Your main considerations are how much water do you think you'll use? A full bathtub is an average of 110 gallons of water, and one gallon of water weighs approximately 8.6lbs. Weight is the second most important factor; Where and how can I support the weight of carrying water? Most RVs have a solid plastic water container that stores around 40 to 80 gallons of fresh water, and have a direct hookup for water when they park at campsites.

I've designed my build to be completely off-grid, boondocking only. I wanted to be able to go out into the desert somewhere for a couple weeks and not have to worry about spending $25 a night to stay in some campground. So how do you do that?

Usually water tanks are solid plastic containers that are mounted somewhere on the vehicle, perhaps underneath, and have a water pump with an accumulator tank attached to pull the water out of the tank and into your pipes in your RV. The problem with carrying large amounts of water around is it's weight while you're driving. If the tank is half full then the sloshing momentum of the remaining water can cause problems (apparently). 

I bought a food safe water bladder instead to use as a water tank, and built a storage compartment with the bladder inside so the bladder can only expand to the container's dimensions, and the weight of the water will always be distributed as low and as flat as possible. If I had the ability to weld a storage cage underneath the truck for the water, that would have been ideal.

BayTec Container's Aquatank Water Bladder.

I originally wanted 80 gallons of water storage, but decided later on to move the tank to the rear of the truck and cut the size down to 60 gallons. Since my bladder was a 150gallon capacity, I had to find out how big the inside of the container should be so that it only can store 60 gallons. You can convert the volume of liquid to cubic feet to better understand how much 3D space a gallon would take up.

 

https://www.ginifab.com/feeds/cbm/cubic_feet_calculator.html

I played around on this site for a while until my dimensions matched the cubic ft requirement I needed for 60 gallons.

Now I knew the size, so I started to build the storage container for it. Your water tank needs the inlet to be higher than the rest of the tank, and your outlet to be at the lowest point.

Building The Tank:

Base plate with corner support brackets

 I wanted the tank to have a larger base on the bottom than the actual storage box so that it could more evenly disperse the weight and be able to bolt it down. I used 3/8 OSB and marked the dimensions of the box itself on the base.

You'll need a circular saw to cut these panels - adjusted to 1/4 inch thicker than the material

I left two inches around the tank to be able to bolt it down later, with a larger space on the outlet side

The reason I left a larger space on the outlet side is so I can add a pipe that the outlet tube will rest in. The idea is to stop the outlet tube from getting pinched when the tank is full and it will hold it in place.

Outlet tube - 1.5inch diameter PVC with waterproof flashing tape on the edges

Internal framing for stronger corner support while driving

Adjusting the bladder and adding insulation

Here you can see the inlet. I'm going to add a 2 inch diameter pipe with a cap on the lid that the inlet will rest inside off

Here is the lid before it's screwed down. I used 2 inch pipe as the entrance for the inlet, but I would recommend only using PVC because it rusted on part of the threads within six months

I added an extra drain plug on the bottom in case the bladder ever broke for some reason to drain excess water

The wood on top is to create a slant for the roof of the tank so water doesn't pool on the top. The inlet is capped off with a 2inch female threaded cap

Galvanized sheeting used as the roof of the tank with silicone on the edges

The bolts go through the metal bracket, through the base, to mount the tank. Two for each corner

I painted all of the OSB with a rubberized roofing sealant (paintable), and eventually painted with normal external paint. This has held up for at least two winters already, so going good!

An oversight of mine, after the tank was made, was how much space the framing took on the inside. This brought the internal dimensions down to about 6 Cubic ft - making the water tank a 45 gallon capacity instead of 60 gallons. It's still an acceptable size, and brings down the weight, but remember to include the framing in your dimensions!

Mounting the Tank:

Originally I planned to carry my motorcycle on the back of the truck, but it ended up being too heavy for me to lift safely into place after I built the carrier. After driving the truck and how bumpy it was - I was very glad my motorcycle wasn't on the back and my water tank was instead. It held on great and seems to be an ideal place for it. Here's how I mounted it!

My original idea for the carrier with my propane storage on the end

The base framing for the carrier are 4 x 4s, bolted through the rear step of the truck

Originally the propane storage was pushed out farther, but I cut new pieces and extended the width the entire way

Two bolts per 4 x 4 - ten total

I used Grade 8, 5/16th diameter coarse thread bolts with locking nuts to secure the 4 x 4s to the step. It was surprisingly easy to drill through the step. I cleaned the holes and sprayed anti-rust paint on the step before I added the 4 x 4s

On top off the 4x4s I screwed down pressure treated 2 x 12s cut the full width of the carrier. (which is slightly less width than the truck so it's not damaged while turning).

I used three 2 x 12s with about 1/4inch between them for water drainage. All 4 x 4s are cut to the same length and the base plate for the water tank is bolted through the planks with grade 8 bolts and flanged locking nuts.

Here you can see the water tank resting on top of the three planks

I'm direct plumbing a 1/2inch PVC line from the outlet of the tank through the rollup door wall, into a shutoff valve, and then into my water pump. My water pump is self-priming up to six feet, meaning it will pull the water from the tank up to a maximum height of 6 feet away from the tank - which is no problem for me since it's about a 3 foot difference.

This has held up well so far and I'm planning to add a pipe warming kit to the outlet pipes. I'll show you how I'm doing that in a couple weeks or so once it's warm enough to re-do that plumbing. Otherwise the only thing I think I'll change is adding some flat washers to the bolt heads holding down the 4 x 4s so there's less chance of the wood cracking.

Otherwise I hope this helped you with your tank or gave you an idea for rear storage on your vehicle! If you have any questions, feel free to ask.

Sincerely,

Kelli