I was not suggesting any actual change, merely pointing out some maths that feeled strange. But as I've said, I"m ready to dismiss this on the count of gameplay and fun.
That being said, it would indeed be a possible fix.
So following your idea, there should be at least 3 rain collector :
The small colletor in a box like fashion with about the same capacity of 160 water unit (volume of water = 27 cf - [1/2 * [4*pi*1,5*1,5*1,5]/3] = 19,93 cf or about 8 wu/cf)
The rain barrel that would have around 250 water unit capacity and be a 3 foot diameter barrel of roughly 4 foot in height (do the math)
A large multi tile (minimum 2) collector that could be built with tarp AND plastic bags/garbage bags for joints. It would be 3x6x4 minimum, with possible additions to it. A single tile capacity (minimum 2) would be roughly 275 water unit (or 550 for a single 2 tile collector). It could take advantage of the upcoming building mechanic where you can upgrade structures. Maybe it could even need some duct tape
Edit : Those maths are based on the actual capacity and figured volume of collectors. Overall it seems that collector have a much lower capacity then their figured volume would warrant. For example, a simple bottle hold 40 water units. Assuming it's 500 ml, it's 0,1766 cf or about 226,5 wu/cf! Now we can assume that a collector has lost spaces and framing... but nothing that would justify this variation.
To solve this, they could just make the large rain collector barrels two tiles. Perhaps more of a trough than a barrel... Plastic sheets could be added to the game to make it more realistic, difficult, and desirable to build.
Edit: come to think of it, perhaps a tarp would work with a reduced complicity vs a large plastic sheet...
I love being weird, unless there are children or doppelsoldner drug friends hanging around my house. However this doesn't prevent them from noticing the strange things that try butt chocolate. I'm a curious hadephobic pagan who buys people from Japanese traffic-rings freedom, that is
Changed to Hadephobic for funniness (sorry footmuffin)