Foreign Minister Vivian Balakrishnan has called Malaysian Prime Minister Mahathir Mohamad's pointed comments over the 1962 Water Agreement a "red herring".

Referring to Tun Dr Mahathir's remarks on Thursday urging Johor's government and people to protest against what he called a "morally wrong" pact, Dr Balakrishnan said the words used were "strong, emotive" and intended to rouse public opinion.

Dr Mahathir, in urging Johor to protest the agreement, had questioned how "a rich nation" could pay "such an unreasonable rate" for raw water sold by Malaysia.

Dr Balakrishnan told Parliament that Singapore's position on the water pact has been "clear and consistent". Neither Malaysia nor Singapore can unilaterally change the terms of the agreement between their countries.

He said Dr Mahathir himself had explained in 2002 that Malaysia chose not to review the price in 1987, when he was PM, because it benefited from the deal - under which Johor paid for treated water at a fraction of the treatment cost.

Dr Balakrishnan added: "I am supposed to be diplomatic. But I think members of this House also know that I call a spade a spade."