I'm a big fan of the plastic Scepter Military Water Canister (MWC) and the Military Fuel Canister (MFC), which are currently used by NATO military organisations. Extremely durable, without the possible corrosion and leak issues of steel designs. New MFCs can be difficult to find in the U.S. due to environmental laws (I bought mine in Canada), but MWCs are easy to get, and at reasonable prices. Used, surplus MFCs are occasionally about, but they were taken out of service for a reason, and I don't like buying someone else's problems.

The standard size, 20 L MWC comes in a variety of colors, and a 10 L size is available. If you don't have a permanently mounted fresh water tank, it's hard to go wrong with one.

As good as an MWC is, there are still times where another solution may work better. Enter the Cornelius keg. I spent more time than I wanted to this afternoon learning the finer points of the Cornelius keg. Perhaps you've seen some of these lurking under a restaurant or bar counter.

Bag-in-Box systems have largely replaced Cornelius kegs for transporting soft drink syrup, but there's a steady demand for the old tanks by home brew beer makers. I've no interest in that, but their popularity makes it easy to find new parts, once you determine what fits your keg.

Dad gave me a keg years ago, and it's been quietly resting in my backyard since. I have a need for another 5 gallons of water capacity, and I decided it was time to turn the old keg into something useful. With a little work and some new parts, mine will be resurrected as a roof mounted, solar heated, pressurized water source for showers & camp kitchen use.

It took several tries to get my order to go through at Corny Keg, but I finally succeeded when using Microsoft Edge. Otherwise, I found the site very informative, with a wide range of parts at reasonable prices. In particular, the Tips page on keg identification was a real find, since there are a variety of Cornelius keg models, with slightly different threads.

Rather than try to rebuild the crusty old pin lock posts on my Corny, I'm replacing them with new ball locks and connectors. I also swapped the old lid for one with a manual pressure relief valve, which will make it easier to depressurize the keg when I need to remove the lid. I'm adding a short Schraeder valve to the lid so I can pressurize the keg with my portable compressor. 

I used a kitchen faucet sprayer with an adapter to transition from the threaded fitting to a 1/4" hose barb. The kitchen sprayer pattern fills bottles & bladders well, and does a good job for dishes & bathing. A bungee or strap holds the tank in the rear cab corner well, and I can remove it for use in a small shower tent, as needed. I need to refine the mount, but a carpet pad cushions it nicely in the corner, and keeps it out of the way of my fridge slide.

Here's a photo a friend of mine took while in the Maze District, Canyonlands NP.

Update: I've used this tank for two weeklong trips, and it does its job perfectly. It hasn't leaked, but I may install a 1/4" ball valve to shut off pressure to the hose when not in use. I used a kitchen faucet sprayer hose, which is rated for at least 50 psi, but I don't want to chance a leak and have several gallons of water sprayed into the truck cab.

Even if all of the parts are bought new, I believe this is a much better value than some of the other options for a pressurized water source. No offense to competing products, but they typically cost more and may not be as hardy. Corny kegs have proven to be very durable over decades of use in the food industry, and for a self-contained solution, there's little room for improvement.