South African President Jacob Zuma “benefited unduly” from a $23m state-funded security upgrade to his private home that included a swimming pool, cattle enclosure and an amphitheatre, the public protector said.

In a report released on Wednesday, just six weeks before an election, South Africa’s top anti-corruption watchdog accused Zuma of conduct “inconsistent with his office” and said he should repay a reasonable part of the cost of the unnecessary renovations.

“The president tacitly accepted the implementation of all measures at his residence and has unduly benefitted from the enormous capital investment in the non-security installations at his private residence,” Public Protector Thuli Madonsela said in her report.

The improvements included a visitors’ lounge, amphitheatre, cattle enclosure and swimming pool, referred to in official documents as a “fire pool” on the pretext it could double up as a water reservoir for fire-fighters, the paper said.

Zuma’s spokesman declined to comment, but the ruling African National Congress (ANC) immediately threw its weight behind its leader, saying it believed he had done nothing wrong.

As the report’s formal release day approached, several senior party officials have appeared in the media questioning the integrity and independence of Madonsela, whose office is enshrined in South Africa’s post-apartheid constitution.

The newspaper said Madonsela’s draft report, entitled “Opulence on a Grand Scale”, found Zuma had derived “substantial” personal gain from the home improvements paid for by the state and recommended he should repay some of the money.

The report, which was leaked early in November, provoked derisive cartoons of Zuma sipping cocktails and relaxing in his “fire pool”, and reinforced the perception of runaway corruption in Africa’s biggest economy during Zuma’s first term in office.

Despite voter concerns about corruption and shoddy public services, the ANC is almost certain to win the May 7 election, handing the 71-year-old Zuma another five years at the helm.

Before the leak, the government had gone to court to try to prevent Madonsela releasing her findings on the grounds that they might jeopardise Zuma’s security. The challenge was dropped after Madonsela made clear there was no threat.

The paper also said Madonsela accused Zuma of misleading parliament by telling it in 2011 that all the buildings in the sprawling compound had been built “by ourselves as family, and not by the government”.

Zuma, a polygamous Zulu traditionalist, has been beset by scandal throughout his political career.

The extent of Zuma’s unpopularity in urban areas was highlighted by the boos that greeted him at a memorial to Nelson Mandela at Johannesburg’s Soccer City stadium in December, although he still enjoys huge support in the countryside.