The Series D funding will help the Irvine, Calif.-based company expand sales of its combination filtration and ultra-violet light water purification technology. Water purification is a growing business both in developed countries and the third world.

WaterHealth International Inc., has a deal for poor rural villages around the world - we'll help you borrow money to buy our water purification systems, and then we'll stick around to make sure they're run properly.

The Irvine, Calif.-based company announced this week it has raised $10 million in a series D round led by previous investors Dow Venture Capital and SAIL Venture Partners.

That brings total investment for WaterHealth to about $26 million, CEO Tralance Addy said Wednesday. The company hopes to raise another $10 million by March.

WaterHealth is among a number of companies, from startups to giants like Bechtel Corp., General Electric and Siemens, that are focusing on the looming worldwide water crisis (see A Guide to the Water World).

An estimated 1.1 billion people worldwide lack access to clean drinking water, and the United Nations has warned that population growth and water depletion could lead to water shortages for 2.7 billion people by 2030.

Founded in 1996 with technology developed by physicist Ashok Gadgil and licensed from Lawrence Berkeley National Laboratory, WaterHealth at first sold its combination water filtration and ultraviolet light purification systems as stand-alone devices, letting the buyers run them.

But that model changed in 2004, when Addy came on as CEO. Now WaterHealth helps rural communities and non-governmental organizations secure loans to build "community systems," which cost about $65,000 and are housed in a garage-sized building, and then sticks around to manage the systems.

"It's a contribution of a whole chain of people looking at what we need to do to be effective," Addy said. "If you rely on other people to supply the other pieces and integrate that, it leads to inefficiencies and higher costs."

WaterHealth has about 600 systems installed around the world in Central and South America, Africa and Asia. Of those, about 300 are the new "community system" model, the majority in India, though a few are installed in Ghana.

Knowing that it is serving communities where people often earn less than $2 a day, WaterHealth helps communities by arranging loans for those that can put together a 30 percent to 40 percent down payment on a system, which run about $60,000 on average. Those loans are backed by $30 million in loan guarantees from Dow Chemical, whose venture capital subsidiary is an investor in WaterHealth.