"Mountains of money are about to be spent on the water industry," says exchange-traded fund expert Paul Tracy.

In his The ETF Authority, the advisor adds, "All things considered, my favorite way to invest in the water sector is through the PowerShares Global Water Portfolio (AMEX: PIO)."

"PIO tracks a benchmark that has delivered the strongest gains in the group by a comfortable margin.

"For the last five years, through the end of last quarter, the Palisades Global Water Index has posted annualized returns of 24.9%, for a cumulative gain of 204% -- versus just 44% for the S&P 500. In other words, a $10,000 investment made in 2003 would be worth more than $30,000 today.

"Yet, the portfolio is still the most attractively valued -- the average holding is trading at just 2.5 times book value and 13 times earnings.

"Shareholders in the ETF will have a stake in companies like Veolia Environment, the world's leading provider of water and wastewater treatment.

"Other top holdings include Kurita, which supplies ultra-pure water for semiconductor manufacturing and makes reverse osmosis seawater desalination systems for remote islands; and Hyflux, a leading maker of water recycling technology used in Singapore and China.