Water in 200ℓ drums is a reasonable thing to want to store in your house, both for drinking and for thermal storage, but water spills can cause serious property damage and even electrical hazards. How can we store it in an inherently leak-safe way?
This is a problem with waterbeds, too, which commonly contain 1000ℓ or so of water. The usual solution with waterbeds is to surround the vinyl bladder with a stiff plywood frame with an impermeable polyethylene liner; this way, when the vinyl eventually ruptures (as warm, plasticized vinyl under continuous stress eventually does) the water will be safely contained within the frame, as long as no holes in the liner have previously escaped detection.
You might think that this solution works so well for waterbeds precisely because the inner water container is flexible — if it starts to leak, the water outside of it will tend to collapse it, and the overall level of water will not rise above the edge of the frame. But a little thought will show that this is a fairly general property of such systems, even if the inner container is rigid. If you have a 200ℓ plastic drum of water standing on end inside, say, a 230ℓ bucket that is as tall as the drum, if water begins to escape, once the water level outside the drum equals the water level inside, it will stop rising, even if the drum is floating at that point (which will happen with polypropylene drums). Hopefully some kind of alarm will have gone off before this point, intake shutoff valves will have been closed, drains will have been opened, etc.
However, an additional layer of protection could be provided by a large tray holding several drums. Consider a rectangular array of N round 200ℓ drums next to each other. Each occupies π/4 of its square cell, 79% of it, leaving the other 21% empty. If you have four such drums in a 2×2 array, the empty space in the tray amounts to 86% of a square, which is 109% of the volume of one of the drums. So, if any one of the four drums breaks open and spills its contents, walls around the four-drum unit up to their height would keep any of it from escaping, even if the bottle were filled with air until all the water escaped. In a 4×4 array holding 3.2 tonnes of water, walls up to ¼ of the height of the drums would be adequate to provide such a containment service against the total failure of any single barrel.
This is not the only safety measure that is needed — as I said, automatic shutoff valves, drainage routes, and alarms are highly desirable, and of course there are the usual issues of cleanliness.
(Relatedly, I’ve previously written about inherently-safe fuel storage by floating small bottles of ethanol in water tanks.)