These include how much residents are reducing their demand.
Phase two will be triggered when the six big dams supplying Cape Town reach a storage level of 13.5 percent.
This leaves just enough water to supply critical services – including sufficient water to distribute to collection sites across the city.
In phase two the plan is to roll out distribution points across the city.
Site selection is unlikely to be evenly distributed across the city, because distribution sites will depend on existing water pipelines.
Avoiding Day Zero Cape Town is using a relatively simple model to manage water in an effort to move circumstances from a critical zone, and potential failure, to a position where the risk of running out of water is greatly reduced.
Reduced demand is one way of postponing Day Zero.
Some irrigation boards have closed off their water supply, and farmers are reducing the amount they draw from the Western Cape water supply system.
A final factor is that new projects will also bring additional water from tapping into the aquifers and from desalination.
There are encouraging signs suggesting that the city will get through this difficult period.