A scarce supply of water may become Cape Town's defining feature, and the city has already been touted as one of the first major cities in the world that could run out of water.

This was the warning from City of Cape Town Deputy Mayor Ian Nielson, who spoke on Sunday at the WISA 2018 Conference, expected to attract 2 000 captains of industry.

The four-day event, which has the theme of 'Breaking barriers, connecting ideas', seeks to shine a light on; and propose solutions to water resource challenges.

"We need to accept that the days of plentiful water supply in Cape Town may very well be over," Nielson said in a prepared speech at the Cape Town International Convention Centre.

Cape Town has been in the grips of a devastating drought for the past three years. It narrowly averted a catastrophe with dam levels bottoming out at 20% - 7% above the level at which disaster would have struck.

Although Day Zero - when taps will be turned off - has been pushed back to next year, residents are still reeling with level 6B water restrictions in force, which means that only 50 litres of water per person per day can be used.

"While we hope at some point in the near future to be in a position to relax these restrictions, we cannot afford to return to our previous levels of consumption."

Last week, Cape Town marked its biggest single weekly increase in dam levels for the year so far when it surged by 6.3% to 38.1% of storage capacity.

"With the recent good rainfall received in June, we have seen a steady increase in our dam levels, but we are by no means out of the woods yet," said Nielson.

However, the deputy mayor cautioned that there was no way of predicting with certainty that the current bout of good rainfall would be seen in July and August.

"Rainfall variation over recent years is greater than anything we have experienced in the past 100 years," said Nielson.

He says that, with rainfall patterns and distribution changing as climate patterns become increasingly unpredictable, it requires a reassessment to the City's approach to water supply.

"We can no longer rely solely on surface water supply [the run-off from rainfall into rivers, lakes and dams] and are therefore driving a supply diversification programme," he said.

"One of our groundwater abstraction projects is producing 12-million litres a day, and will soon scale up to 20-million litres. Other groundwater abstraction projects are under way and we anticipate that at their peak, they will supply around 150-million litres of water per day."

Nielson noted that a third desalination plant was on track to produce water by July.

"As demand for water grows along with our population, it is not only diversification of supply that is required to address future risk, but also a sustained campaign to encourage behaviour change among water users," he said.

"It is now more crucial than ever that we share with others what we have learnt and learn from them in order to craft a common strategic vision on how best to conserve and manage our water resources for a sustainable future."