MANILA - The Philippines' water regulator said on Wednesday it has cancelled the 15-year extension of concession deals it signed with the country's two largest utilities after pressure from President Rodrigo Duterte.

Duterte described the concession agreements with Manila Water Co Inc and Maynilad Water Services as "onerous and disadvantageous" to the public, prompting them to be revoked in a move that could turn off investors at a time the government is seeking foreign capital to modernise its infrastructure. 

Metropolitan Waterworks and Sewerage System, the country's regulator, told lawmakers it had revoked last week a decision extending the water concession deals with the two utilities until 2037, sending their shares tumbling more than 13%. The existing concessions will expire on 2022.

The firms, which are servicing a combined 16 million customers, secured 25-year concession agreements in 1997, which were extended in 2009 by a further 15 years.

Duterte acted after Manila Water and Maynilad won arbitration cases in Singapore against the government.

The arbitration court in Singapore ordered the Philippines government to pay the utilities a combined 10.8 billion pesos ($212.14 million) in compensation. The companies had said they would forfeit any damage claims to avoid angering the president.

"These companies not only have inefficiently delivered water to the households, but exacted unconscionable amounts from the taxpayers," Salvador Panelo, Duterte's spokesman, said in a statement.

The water utilities' woes display a violation of the sanctity of contracts, Guenter Taus, former president of the European Chamber of Commerce of the Philippines, told Reuters.

"It does not instil investor's confidence. You can't just go out and revoke contracts," Taus said.

The embattled companies' shares continued their decline on Wednesday, with Manila Water slumping 14%.

Maynilad stockholders Metro Pacific Investments Corp and DMCI Holdings Inc sank 13% and 13.4%, respectively.

Manila Water president Jose Rene Almendras told lawmakers the company has yet to study the impact of the regulator's decision.

"There should be a clean process because we have commitments both in terms of capital expenditures, projects and loans," Maynilad chief operating officer Randolph Estrellado said.

($1 = 50.91 Philippine pesos)

(Reporting by Neil Jerome Morales; editing by Mike Harrison) ((neiljerome.morales@thomsonreuters.com; +632 8841 8914;))