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Ralston Reservoir Maintenance

Project description

Beginning in October 2021, the Ralston Reservoir will be taken offline and drained for a period of approximately six to nine months in order for Denver Water to perform maintenance activities to the reservoir. Ralston Reservoir, which is owned and operated by Denver Water, has historically been the sole source of raw water for the Ralston Water Treatment Plant (WTP).

Map of ralston reservoir

Ralston Reservoir is located on the west side of State Highway 93. Arvada/Blunn Reservoir is located on the east side of State Highway 93 just north of W 64th Avenue. Arvada/Blunn Reservoir is not being drained. It is operating as usual

In preparation for the maintenance work on Ralston Reservoir, the City team completed construction of a new raw water pump station and pipeline in order to supply raw water to the Ralston WTP from the Arvada/Blunn Reservoir. 

Project timeline

Over the past few months, water from Ralston Reservoir was used by the City of Arvada's two water treatment plants. Beginning October 15 2021, Denver Water began draining the rest of Ralston Reservoir into Denver Water's canal system.

The maintenance work on Ralston Reservoir is expected to take six months.  At the conclusion of the maintenance work, Denver Water will refill Ralston Reservoir. It is anticipated that Denver Water will begin refilling Ralston Reservoir in mid to late April 2022.

Frequently asked questions

Why does my water taste different? 

During the Ralston Reservoir maintenance work, the source of raw water the City treats for drinking water will be Arvada Reservoir. Typically in fall, we are tapering off our use of Arvada Reservoir, however this year we will be using Arvada Reservoir water (treated at Ralston Water Treatment Plant) through the winter and into the spring. You may notice some differences in the taste, as Arvada Reservoir is a warmer and shallower reservoir than Ralston Reservoir. We have been doing additional treatment to the water and continue to perform all the same required tests as well as additional tests to ensure the water we are delivering to you is safe to drink. It may taste a little “earthier” as we get through fall, but the cold weather and seasonal turnover of the lake should correct that issue. Please be patient and rest assured that the water is safe and will return to “normal” soon! 

Where did the water from Ralston Reservoir go?

The water from Ralston Reservoir was used by Arvada's water treatment plants over the last few months. As of October 15, 2021, Denver Water started draining the remainder into their canal system.

Why did the City have to issue watering restrictions? 

With extended hot summer weather, water demand remains high. As Ralston Reservoir is taken off line for necessary repairs, the City will no longer have the capacity to treat the amount of water that the community is using for summer outdoor watering. Therefore, we need the community to reduce their outdoor water usage to no more than three days a week immediately. On October 15, all outdoor watering except for handheld watering must end. Read the full news release on

Does the City have sufficient water supply for residents and businesses during the maintenance work?

Yes, the City has sufficient water supply. Periodically, Denver Water will deliver water from Gross Reservoir to Arvada/Blunn Reservoir.

How does this project affect operations at Arvada/Blunn Reservoir?

Operations at Arvada/Blunn Reservoir are unchanged. The reservoir closes for the season on October 31, 2021 as usual.