The DA in the Eastern Cape claims the Nelson Mandela Bay Municipality only has five weeks of water left.
This, however, has been disputed by the municipality.
The party has called for the City to declare a local state of disaster to mitigate against an impending day zero.
It claims the metro's supply dams are currently at just 22.16% capacity, of which 10% is unusable.
Speaking at a virtual media briefing on Thursday, DA provincial leader Nqaba Bhanga said the metro had been aware a barge was needed to extract what was left of the potable water in the Impofu Dam since August 2018, but no effort had been made to procure it.
He added the Coega Kop Wellfield project needed to augment the water supply to the metro which was still "limping along".
The DA said only 20% of the R200 million drought relief funding by the national government have been spent.
Bhanga added he believed the City was likely to forfeit at least R100 million of the grant "due to the fact that this would be the second application for rollover of the funding".
Phase 3 of the Nooitgedagt water scheme, which provides an additional 70 megalitres, had not been commissioned since June 2019, he said.
"The metro is currently using 300 megalitres per day, where it should only be using 250 megalitres per day. No significant rainfall is predicted for the next six months.
"In order to take quick action, or action that is outside of the ordinary, or to apply for relief funding from the provincial and national governments, it is necessary to have a local state of disaster declared and maintained as long as is necessary."
DA MPL Retief Odendaal said he had approached Water and Sanitation Minister Lindiwe Sisulu to intervene directly.
Bhanga has also written to Eastern Cape Premier Oscar Mabuyane for provincial intervention, however there was no response, he added.
Meanwhile, the MMC for infrastructure, Andile Lungisa, rubbished the DA's claims, saying the municipality would have water supply until January 2021.
He added it had declared a local state of disaster in December 2019.
Lungisa told News24 various long-term projects were planned to mitigate against the drought crisis faced by the municipality, adding this included a desalination plant that would come into effect early next year.
"The DA is playing politics about a human issue. They have run away from standing committees on the question of water. They have run away from a presentation from Kouga on water.
"The municipality was reviving 170 megalitres of water from the Nooitgedagt Dam, with reservoirs in Motherwell supplying parts of the metro."
Lungisa said as part of long-term solutions, the metro had joined forces with the Kouga Municipality and had plans to build a 50 megalitre dam in Kouga.
Nelson Mandela Bay is the epicentre of the virus in the Eastern Cape, with more than 167 cases and six deaths. Statistics released on Wednesday evening indicated the province had 377 positive cases, seven deaths and 15 recoveries.