Opposition Democratic Alliance leader Mmusi Maimane praised residents of Cape Town for slashing their water consumption.
"If we keep consumption this low for the weeks and months to come, we will defeat "Day Zero" in 2018," Mr Maimane, whose party runs the Cape Town municipality, said.
The Democratic Alliance party also tweeted the city had saved 529 million litres of water a day for the past week.
Should "Day Zero" arrive, most Cape Town residents would be forced to queue at communal taps at 200 water points - likely under police or military guard - to collect a daily ration of 25 litres.
A single toilet flush roughly uses nine litres of water.
South Africa's Sunday Times newspaper recently ran an article titled How to shower‚ wash hair‚ shave‚ flush loo on five litres of water.
"[Cape Town's] crippling drought has spawned a multitude of innovative ideas and DIY projects‚" it said before sharing several tips such as using shower water to flush the toilet.
Cape Town officials have said "economically essential" sites will be spared the shut-off on "Day Zero" as will impoverished informal settlements that already rely on communal taps.
But the new "Day Zero" announcement also came on the same day South Africa elevated the drought to a "national disaster" after reassessing its "magnitude and severity".
The government statement, published in the official government gazette, means the national government is now responsible for tackling the issue and ensuring relief efforts.
Rains in Cape Town over the weekend raised hopes that the situation would improve, but the downpours were neither heavy nor long enough to have an impact on the situation.
- with AFP