A sputtering, underwhelming ‘water year’

A winter snowpack that swiftly collapsed in the spring, and a summer monsoon season that was mostly a no-show made for a tough water year at Denver Water.

As the 2024-25 water year ended Sept. 30, Denver Water’s mountain storage reservoirs were below average levels. And the year continued an overarching dry trend, starting in 2019, in the two major river basins where Denver Water collects and stores its water.

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The water year runs from Oct. 1 to Sept. 30 and marks the way hydrologists and water planners track supplies. It essentially runs from the start of snowfall season in the high country through the heat of summer and heavy irrigation months, following the annual pattern of building up a water supply to meet ensuing demands.

Fortunately, despite a drier than normal year, Denver Water’s supplies remain in reasonably good shape, thanks to a robust collection system designed to weather seasons of drought. On Sept. 30, at the official conclusion of the 2024-25 water year, Denver Water’s reservoirs stood at 84% capacity, five percentage points below the historical average of 89%.

“We have been through another warm, dry year,” summarized Nathan Elder, Denver Water’s manager of water supply. “In the last six years, streamflow in Denver Water's collection area has been below average. It’s a trend we can expect to continue in this era of climate change.”

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Months ago, as winter turned to spring, things looked better.

Snowpack was at average levels in the Colorado River Basin, though below average in the South Platte. It appeared winter’s bounty would be good enough to fill Denver Water’s reservoirs to full capacity.

Then came a dry spring and a monsoon-less summer on both sides of the Continental Divide. The lack of precipitation increased demand from customers for water to use for irrigation, had farmers calling for more water, and reduced runoff volumes in mountain streams. Reservoirs that had been predicted to fill instead fell short. 

Some facts that capture the tone of an underwhelming water year.

• Poor Front Range water supplies and senior “calls” from farmers who are first in line for water put pressure on Dillon Reservoir in Summit County. Demand for its water in a dry spring and summer meant Dillon’s reservoir levels fell below optimal for its marinas, as did outflows for Blue River rafting.
• The South Platte River flows were so poor it saw farmers invoke an 1864 right for water in late August, the oldest right invoked since an 1861 right in 2018. All that translates to anemic river flows that had enough water to fulfill only the very oldest water rights in priority, leaving other users, like Denver Water, dry. Typically, the river carried enough water that it could meet requests from far more “junior” rights dating to the year 1900.
• In what used to be a once-in-a-decade scenario, Denver Water, under agreements with other entities, was required to release water from its West Slope reservoirs to help make up shortages in the Colorado River Basin. Such “substitution” releases have now occurred three times since 2021.
• Precipitation was poor on both sides of the divide until late August. In central Denver, rainfall from June 1 to mid-September was 3.6 inches, more than two inches below the 5.73-inch average. 

Yet, while a lack of rain in the metro region can typically drive water demand higher, Denver Water customers continued to do a good job conserving throughout the dry summer, barely pushing usage above the five-year average. Customers followed Denver Water’s annual summer watering rules, turning off their sprinkler systems in stormy periods and even changing out turfgrass for less-thirsty alternatives.

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There were other brights spots. 

Denver Water’s supplies, though stressed from the dry spring and summer, held up well even as water levels at one of the utility’s key reservoirs, Gross Reservoir in western Boulder County, continues to be held at only about two-thirds of that reservoir’s existing storage capacity while a project designed to raise its dam and expand its storage capacity continues. 

At the same time, Denver Water continues to improve capacity in its downstream reservoirs, northeast of its service area. Those facilities, which capture and store flows from the South Platte River when conditions allow, give the utility more flexibility to address calls for water from farmers downriver without tapping other supplies.

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And based on historical data, Denver Water still has about a 90% chance of refilling its reservoirs next summer, though warming spring seasons driven by a changing climate add uncertainty. 

Perhaps the most hopeful note: September.

The month had been trending hot and dry but in 2025, it was wetter and cooler, with a soaking on Sept. 23 setting a daily rainfall record for Denver and stacking early snow across much of the high peaks. It also marked the first September in 14 years that was cooler than average in Denver, by one-tenth of a degree, at 64.7 degrees.  

9News meteorologist Cory Reppenhagen honored the month with an on-air haiku, recited while standing atop Berthoud Pass during the Sept. 23 snowstorm: “Stunning start to snow, break from sizzling Septembers, seasonal throwback.