Dr Mahathir challenged the city-state to survive on processed sea water, after Singapore, which buys about half of its water from Malaysia, queried the price.

Even if we raise the price, by comparison to our national income, it is a very minute fraction. We're doing them a favour

Malaysian Prime Minister Mahathir Mohamad

Malaysia wants to increase the price of the water.

In response to the water fight, Singaporean officials have proposed drinking treated waste water which the government has named NEWater.

Singapore Prime Minister Goh Chok Tong told a Malaysian trade minister on Monday that Singapore would favour using its own water after a water pact with Malaysia expires in 2011

Calling Singapore's bluff?

Prime Minister Mahathir retorted on Tuesday that his country was not bothered if Singapore pulled out.

"Even if we raise the price, by comparison to our national income, it is a very minute fraction. We're doing them a favour," he said.

But he dismissed fears that Malaysia would leave Singapore with no water.

"The fact is that according to the agreement, we must supply them with water - unless we go to war with them," he is reported to have joked.

Price freeze

The price at which Singapore buys water from Malaysia - three sen (0.8 cents) per 1,000 Imperial Gallons (1,200 U.S. gallons or 4,540 litres) of raw water - has been frozen since the early 1960s.

Dr Mahathir stresses that Hong Kong pays mainland China eight ringgit ($2.10) - more than 260 times what Singapore pays Malaysia - for the same amount of water.

Malaysian Foreign Minister Syed Hamid Albar said on Tuesday that negotiations over the water would continue at a meeting in Singapore next month.