Trading houses Mitsui & Co. and Marubeni Corp. plan to up investments in water projects to benefit from global spending forecast to reach $1.2 trillion by 2025.

"We now have the knowhow to take the lead on projects, allowing us to move into the global water market," Koichi Wakana, general manager of Tokyo-based Mitsui's water unit, said in an interview.

Mitsui, Marubeni and worldwide rivals are competing for water projects and government asset tenders to lock in stable income streams and tap a rise in spending in Asia, the Middle East and South America. China needs to build as many as 300 wastewater treatment plants a year to meet government targets, according to Global Water Intelligence.

"Potentially, sewage treatment is where investors want to be looking," said Simon Powell, head of sustainable research at CLSA Ltd. in Hong Kong. "That's where the infrastructure spend will be."

Mitsui and Tokyo-based Sumitomo have submitted bids for a $250 million tender to build and operate a wastewater plant in Bahrain.

The bidding, involving six groups, should be decided by June, Hideki Yamano, the head of Sumitomo's water business, said in an interview.

"The timing is right to increase our water assets either through new projects or acquisitions," said Yamano.

Global freshwater needs may triple by 2030 and Asia will be the region with the fastest-growing demand, according to General Electric Co., which provided water-filtration technology for the 2008 Beijing Olympics.