Here is an article for you about cisterns.
Cisterns have been used for water storage for thousands of years and continue to be used today. A cistern is a large water storage container that is often underground. Many of you will remember Masada where the Roman Legion had the Jews besieged. This mountain top fortress was able to hold out for as log as they did, in part, because of the large cisterns where they stored rain water. In fact without cisterns this would have been nothing other than another uninhabited mountain.
These water storage tanks can range up to thousands of gallons, or liters if you prefer. The size of your cistern should be determined by your water usage and the water source. If your water source is seasonal then a large enough capacity to get you through the dry spell would be real nice. A cistern can be above ground, below ground or partially buried. This storage is something of a midpoint in you water system sitting as it does, between the collection and distribution systems.
I grew up in a community where thousands of homes collected their water off the roof and stored it in a cistern. I have seen, used, and built many different cisterns. The first one I actually put together was an inexpensive above ground pool. We made a level spot near the eve of the roof and ran the down spouts from the gutter into the pool. While today I might question whether the plastic liner was appropriate for potable water, back then the question never came up. We drank from that pool for years and it didn’t affect me… affect me… affect me. Actually because of the price and ease of installation this type of cistern became fairly popular around the community for a couple decades. While they will last for a few years the plastic eventually deteriorates in the sun or the thin metal sides rot out so this is not a permanent solution. In a SHTF scenario your down spouts could be run to your in ground pool to collect what ever rain you do get and replenish what you have consumed. If this becomes part of your plan you might want to secure and store adequate downspout and/or pipe.
Another popular way to build a cistern is with a ten foot length of culvert. The suppliers would nest these starting with an eight foot culvert inside a larger and larger culvert till the largest was about twelve feet across. This greatly reduced shipping cost. Since the freight company cubes something like this you are essentially paying freight for only the largest culvert. The culverts need to be manufactured in such a manner as to have water tight seams. Delivered laying on its side it could be transported on the road with little problem. When placed on a low trailer the twelve foot height would fit under the power lines and the ten foot width was legal. The process is to dig a flat spot larger than the culvert to a depth that the top of the culvert will be lower than the eve of the house. You then make a form for your concrete and place reinforcing inside the form. Pour and level your concrete. Tip the culvert into the wet concrete and vibrate it to create a seal. The culvert should set so that it is four to six inches into the concrete. After a week or so the concrete has cured enough to start filling your tank.
The tank off an old water truck was a quick answer in that it only required a flat spot. I would expect an old milk truck tank to work as well. A local mill had been serviced by a four foot diameter wooden water line. We wound up with a twenty foot section and built ends in it.
A friend of mine built a tank out of plywood and put a plastic liner in it. He started with eight sheets of plywood. Standing up two on each side he attached 2X6’s every foot from the bottom past midway up then spaced them further apart. The 2X6’s were laid on their side, run past the plywood and bolted to the intersecting 2X6’s. This is a relatively inexpensive tank but be aware that eight feet of head generates quite a bit of pressure at the bottom so do quality work. Stringers tying the bottom sides together are essential as well as the top.
The newer systems often choose the plastic tanks made for that purpose. The largest of these are cylindrical. A buddy of mine had room to place two, five thousand gallon tanks behind his house. There was a small ledge on the hillside next to these that allowed him to place another two thousand gallon tank. With twelve thousand gallons available they can go quite a while without rain.
My personal favorite is to build the cistern as part of a concrete foundation. This requires a foundation of at least four feet tall to get adequate volume. A full basement would be even better. If this is the way you go I strongly suggest that you design the house so that no sewer lines run above the water tank. This leaves your entire water system accessible inside the house and protected against freezing.
One of the problems with outside water storage is the possibility of freezing. I had an eighteen hundred gallon plastic tank freeze solid one winter with no apparent damage. It was not in current use and had been filled without my knowledge so I did not know to empty it. This tank had also been sprayed with four inches of insulation so it took over a month for it to thaw completely in the spring. Insulating a tank can help as can putting it in a shed. Two or three wraps of PEX pipe around the outside near the bottom before you spray the tank works well if you have a boiler. Your outside water storage could then be another zone off the boiler. My outside tank has seen -40°F with no problem. Okay, maybe a few problems but I worked them out.
If you do not have really severe winters a heat tape on a Hula Hoop will keep your tank from splitting. Just a heat tape on the water line will leave an open passage that allows the water to escape out the top if the ice expands reducing pressure on the tank walls. You still lose that volume of water that turns to ice. At least until it warms up. We had a particularly long stretch of cold weather this year and a neighbor of mine ran the water from his water heater back into his tank to melt some of the ice and reclaim some of the lost volume. You can also put a purpose made electric heater in your tank. If the bottom of the tank is buried below the frost line freezing problems are greatly reduced. These are some of the heat sources at your disposal if you opt for outside storage.
https://survivalblog.com/water-cistern-facts-by-rex-x/
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news for yall. We are getting more laws and taxes here every year. Half our phone bill is taxes. 
