Fort Collins -- Some northern Colorado cities are earning thousands of dollars selling water for use in hydraulic fracturing or fracking.

The Fort Collins Coloradoan reports the town of Windsor sold more than 8.4 million gallons for nearly $17,000 between Nov. 1 and March 1.

In all of 2011, Greeley sold more than 491 million gallons, mostly to the oil and gas industry, for $1.6 million.

Fracking uses pressurized water, sand and chemicals to crack open fissures within wells and improve the flow of oil and gas.

Colorado regulators project that about 5.2 billion gallons of water will be used this year for fracking statewide, compared with 4.5 trillion gallons used by agriculture each year.

Some conservationists argue increasing use of fracking could consume more water than the state can spare.