Ghana's minister for works and housing, Kwamena Bartels, told a news conference the government in his country was encouraging local authorities to adopt regulations to enforce water harvesting.
"In the colonial era... every house harvested rainwater, but don't do it now, because we have piped water," he said.
"If we could get every house to harvest rain, at least for uses other than drinking, such as cooking, cleaning, and watering lawns, the stress on treated water would be reduced."
Bartels was in New York to attend a three-day special session of the United Nations General Assembly on the problems of increasingly large cities and of the 1.2 billion people who are without adequate shelter.
UN Secretary General Kofi Annan told the opening of the session on Wednesday that public-private partnerships, empowerment of women and extended property rights were among ways of confronting the problems.
He noted that two-thirds of the cities in developing countries did not have waste-water treatment.
Bartels said daily demand for water in the capital of his country, Accra, was estimated at 94 million gallons (427 million litres), but supply was 60 million gallons (272 million litres), up to half of which was unaccounted for.
Losses were caused by leakages and illegal connections "some of which are effected by officials of the Ghana Water Company itself, for private gain," he said.
Accra is one of seven demonstration sites chosen by the Water for African Cities programme of Habitat, the lead UN agency for coordinating activities on human settlements, which organised the special session. The other demonstration cities are Abidjan, Addis Ababa, Dakar, Johannesburg, Lusaka and Nairobi.
Habitat said eight out of 29 African cities in a 1990 survey suffered from water stress or water scarcity. It added that by 2020, it expected the number to rise to 20, as the continent's urban population quadruples from 138 million to 500 million in the same period.
Bartels said 1.5 billion dollars was required to upgrade the water and sanitation infrastructure of Accra, but that kind of investment "will not be met by government alone."
The Ghana Water Company had pre-selected five private companies for tender this month, he said.
"We have calculated that at 63 cents a cubic metre it would be profitable for a private company to invest, but we want to have certain landmarks in place before we allow a private supplier to charge the full rate."
The price paid by the poor for water delivered by tanker what up to five times higher than what the rich paid for piped water, he said.
Private suppliers would be regulated to prevent them charging more than the urban poor could afford, he said.
A "lifeline tariff" existed for dwellings consuming less than 2,220 gallons (10,080 litres) a month, he said, but most families lived in family homes that housed 20 or 30, or even 50 people, whose collective needs exceeded the limit.
Victor Kanu, a senior education specialist in Zambia, said: "We must take care of our resources, which are so limited, that is the crux of the matter."
He said "our traditional values were once very effective in ensuring that water was conserved and not polluted", but said "nowadays there is a lot of stealing, even at very high levels."
This included "tampering with meters by officials, who undercharge consumers in exchange for bribes," he said.
Education in traditional, even colonial, values has a part to play beside billion-dollar investment in solving the water crisis in African cities, experts attending a UN conference said Wednesday.