Gross Reservoir Expansion Project

The Gross Reservoir Expansion Project will help protect against drought and insulate Denver Water’s more than 1.4 million customers against potential catastrophic events such as wildfires and climate change.Denver Water is preparing a major construction project, one that will provide more water to customers while improving the Colorado River and create a net environmental benefit for the state.

The Gross Reservoir Expansion Project — also known as the Moffat Collection System Project — will pave the way for Denver Water to nearly triple the capacity of Gross Reservoir, located in Boulder County.

The need

The Gross Reservoir Expansion Project will address a looming supply shortage and improve the reliability of Denver Water’s system, which serves 1.4 million people in the Denver-metro area. The expansion project will help resolve three major challenges: 

Vulnerability — We need to balance our north and south supply systems. Customers receive 80 percent of their water from the south end of our system. The other 20 percent comes from the north side, through the Moffat Collection System. This imbalance makes the system vulnerable to catastrophic events, such as the Buffalo Creek and Hayman fires, which caused massive sediment runoff into reservoirs on the south side of our system. That runoff forced us to rely heavily on a water-short north system for a period of time. Expanding Gross Reservoir on the north will help balance that inequity.

Reliability — We run the risk of running out of water on the north end of our system. During a severe drought, there is not enough storage on the north to supply water to customers in areas such as northwest Denver, Arvada and Westminster. Expanding Gross Reservoir will make the north side of our system more reliable.

Water shortfall — Denver Water provides water to the more than 1.4 million residents in our service area today, and must prepare to provide water to many of the more than 7 million who are projected to call Colorado home in 2030. Current models predict a significant future shortfall in our water supply. Expanding Gross Reservoir, paired with aggressive conservation and water recycling efforts, will help meet that shortfall.


Denver Water analyzed many alternatives to seek a balance between the cost of the project and protecting the environment. Recently, we’ve developed a detailed cost estimate based on additional design information. The project is now expected to cost about $380 million, which includes design, management, permitting, mitigation and construction costs. This project cost aligns with similar small and medium-sized water projects along the Front Range. As a public agency, Denver Water is funded entirely through rates, new tap fees and the sale of hydropower. No tax dollars are directed to Denver Water or to the expansion project.

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