Here’s a primer of sorts dealing with municipal water supplies for Front Range cities, from Doug Nichols writing for the Berthoud Recorder. From the article:
Here in Berthoud, our municipal water supply comes from the Western Slope (where at least the snowfall was consistently good). It is piped to Carter Lake, and from there to a reservoir where it is treated before heading to our homes.
Denver also gets its water from mountain snows, but some metro suburbs are facing a great dilemma as their supplies, which come not from the mountains but from groundwater pumped from wells, are becoming increasingly scarce. People sometimes visualize groundwater as existing in underground pools or lakes, which deep wells can tap. That is not at all the real situation. Groundwater is present in buried layers of rock called aquifers, where it exists in a manner similar to what it would be like if you filled a bucket with sand and then added water to it. Furthermore, the aquifers beneath Denver and its suburbs are not great tabular bodies of rock extending throughout the region, as once thought. Recent research is showing that some of Denver’s aquifers are essentially buried alluvial fans with limited geographic extents. An alluvial fan is like a river delta on dry land and formed at the base of the mountains that existed to the west of the present-day Denver metro area millions of years ago. The aquifers are now buried as much as 760 m (2,500 ft) below the present land surface. They contain finite amounts of water, which have been there for tens of thousands of years. These supplies are rapidly diminishing as municipal pumps work to provide water to homes and lawns.