Most important thing if you live in a house, get a couple of rain barrels - Even though there hasn't been much rain, when it does rain, those barrels will fill up quickly.
Use grey water for plants and general outdoor use - for instance dishwater should be put in buckets or containers instead of letting it run down the drain. Do the same for shower or bath water. Put a tub inside shower, to catch water when you shower and if you bath, transfer water afterwards to containers or buckets.
Stop using washing machines and dishwashers. Do washing and dishes in tubs instead.
If you drink sodas on a regular basis, make a habit of cleaning the 2l bottle once its empty and immediately fill the bottle with tap water and store it away. In no time you will have a good emergency water supply.
Don't flush the toilet every time you urinate, only flush after using it a couple of times and its also a good idea to use a bucket of water instead to flush, so that you can control how much water you use to flush. Also good to urinate in a bucket instead and then dilute it 1 to 10 with grey water and use that to water your plants, good fertilizer.
If things get really bad, you can use a tarp or even plastic sheet, to collect water overnight from the air or if you have quite a bit of money, you can buy a water from air device. It is on my wishlist of things I still want to buy one of these days..
www.waterfromair.co.za/
If you don't have R26 500 laying around, then I guess you and a couple of friends or neighbors can always club money together and then buy one of the machines.
Since you are in Cape Town, look into pricing for small scale desalination plants. I have no idea how much they are, must be very expensive. I read an article a while back about a guy and a couple of his neighbors who put together a small plant, somewhere in the northern cape if I remember correctly and it supplies them all with drinking water.