Earlier this morning I posted about alternative ways of catching rainwater - especially for those unable to afford rainwater tanks.
I now have another proposition / idea for you.
Long term, water scarsity is going to figure prominently in Cape Town - if not South Africa as a country. Going forward everyone will need to become more water self-sufficient and plans need to be made by EVERYONE - NOW - for your futures. Budgeting, making plans and actioning those will stand you in good stead and ensure that you can help yourself to at least provide some of your water.
So, my suggestion is this - build you own rain water container 😜
Option 1: Either budget to buy a couple of cement blocks a month and, when you have enough, make a partially submerged rain water storage tank - as in pic 1.
Option 2: Alternatively, collect as many plastic bottles (of the same size, naturally) as you can, dig a small-ish / shallowish hole (aim for either a finished structure of approx. 1.0 X 1.0 X 1.0 mtr [ = 1kl storage] or 1.15 (w) X 1.15 (b) X 1.0 (d) mtr [ = 2.25kl storage] in a corner of your garden (where previously you had lawn), and then use that sand you extract from the ground to fill plastic bottles and use them as "bricks - as in pic 2. ( the idea comes from https://insteading.com/blog/plastic-bottle-homes/ )
Both would obviously need "plastering" inside, as well as the addition of a coat of pond paint to make it watertight. (Pic 1 is going to cost you - not only for the bricks, but also for the cement plaster. Pic 2 option is not going to cost you that much - just mainly for the plaster. Both will cost you some time though 😉
Both "containers" would also need a very secure lid to prevent animals / small children from drowing.
Please note: I am merely supply a concept / idea for an affordable water storage vessel - it is up to you to establish if you are legally allowed to do this.
My last hint is: decide what is going to be your secure lid, and work around that. There is no point in making something that you are unable to fit a secure lid to 😉