When asked why investment in clean tech (such as solar energy, water purification systems and alternative automotive fuels) is on the upswing, Silicon Valley's venture capitalists don't hold back. In today's New York Times, the answer is generally the same: profit. Furthermore, some leading VC firms say that underserved populations are the key to unlocking the markets for water and energy:

"When you're talking about energy, when you're talking about water, you're talking about the largest markets in the world. The reason we're allocating dollars to this sector is we think we can deliver attractive returns. It's not because we want to do great things for the environment or great things for the world, [though that is a] great byproduct."Small companies have been working in underserved, developing markets for some time, rolling out distributed solar energy; low-cost, high-tech water filtration; and high-efficiency stoves. What these companies have failed, in large part, to achieve, is scale. With the attention of major venture capital firms, maybe that's about to change.

"You look at all the development that's going on in China and India right now, and you realize that two-fifths of the world's population is going through the kind of industrialization that one-fifth the world's population experienced in the 20th century. The size of the opportunity here is immeasurable."