The History of Longmont’s Water Supply

Many visitors to Longmont often ask, “Where do you get your water?” Well, it’s not a very easy question to answer. The short answer is from the Rocky Mountains. The long answer is complex since Longmont’s water supply includes, “an extensive portfolio of water rights including decrees for pipelines, storage reservoirs, irrigation rights and contract rights, as well as conditional decrees and applications filed in Water Court.” (Source: City of Longmont) Here, we dive into the long history of Longmont’s water supply.

In 1871, when Longmont was founded as the Chicago-Colorado Colony, water was supplied from an irrigation ditch, known as the Longmont Supply Ditch, and from the St. Vrain River. As the town grew, water became less potable. A water wagon from Lyons, Colorado (just west of Longmont) supplemented the city for a while, but even that couldn’t keep up with growing demands.

The city’s founders realized that the crops would need irrigation in order to grow and a more advanced water system would be needed. So, a network of ditches and lakes was planned for the city. Ditches were dug throughout the city, and they were given community and area names: Pella, Left Hand Island, Oligarchy, Clover Basin, Rough and Ready, St. Vrain, Ni-Wot, Swede, Last Chance, and Longmont Supply. Today some of those ditch names remain.

An early Longmont dam located seven miles west of Lyons along the St. Vrain River. Photo: Longmont Museum & Cultural Center Archives

On September 8, 1879, the 300 block of Main Street caught fire and was completely destroyed. The only water for fighting the fire came from the town pump, located in the center of town at the corner of 4th Avenue and Main Street, and a bucket brigade that formed from the St. Vrain River. The fire led to the formation of the first firefighting company in 1880. The fire of 1879 and the recognized need for a clean water supply were the impetus for developing a water system. On April 1, 1882, the Longmont taxpayers voted for a $70,000 bond to build the first pressurized waterworks system.

A six-inch pipeline was built from south of Lyons to the current site of Price Park. That pipeline was sufficient for about 25 years, until further growth and the start of the agriculture boom (including the addition of the Great Western Sugar Factory) created the necessity of building a 12-inch pipeline into town. By 1912, the city had built a hydro-powered electrical plant, and McCall Lake served as a substantial resource of the water system at a volume of 500 acre-feet.

The construction of Longmont’s water tower in Price Park, 1939. Photo: Longmont Museum & Cultural Center Archives

Water security continued to have its challenges throughout the early- to mid-20th century. In 1965, Longmont combated this issue through passing a $6 million bond to build the Ralph Price Reservoir and Button Rock Dam. The city also adopted an annexation policy that required newly acquired areas to surrender their water rights to the city.

Today, the Longmont and Ralph Price Reservoirs along the North St. Vrain River, about seven miles west of Lyons, serve as the city’s water utility storage. Both reservoirs are located in the scenic Button Rock Preserve, a walk-in only natural park, managed by the city that offers trails, fishing and wildlife viewing. For more information on visiting Button Rock Preserve, click here.

Button Rock Preserve Photo: ProTrails

Longmont’s Union Reservoir, located about three miles east of downtown Longmont, also serves as raw water storage for northern Colorado. Water from the reservoir is primarily used to irrigate farms along the South Platte River south of Greeley, Colorado. In 1986, the City of Longmont applied for enlarging this reservoir from 12,000 acre-feet capacity to 32,000 acre-feet capacity. This increased capacity would provide the City with additional water storage capacity, better water exchange possibilities and storage space for reuse water. It would also provide additional recreational opportunities for residents and visitors.

A private irrigation company, the Union Reservoir Company, owns the land inundated by the reservoir along with an additional 90 acres of dry land surrounding the body of water. In 1996, Longmont’s City Council approved a land acquisition and finance plan to purchase the land surrounding Union Reservoir, which was estimated to take 10-20 years. Through the purchase of shares in the Union Reservoir Company and through the transfer of shares to the City as a result of the Raw Water Requirement Policy (City of Longmont, 1964), the City has become the majority owner of the shares of Union Reservoir. Today, the City owns 85% of the shares in the Union Reservoir Company, and property is currently being purchased on a willing seller/willing buyer basis. The City has purchased approximately 265 acres of property around the reservoir. Enlarging the area is still a proposed future city project.

Union Reservoir

In the fall of 2017, Longmont voters approved an issuance of $36.3 million in bonds for the development of a new raw water storage reservoir known as the Windy Gap Project. The reservoir will be constructed north of Longmont, just west of Carter Lake in Larimer County, and it will secure a capacity of 8,000 acre-feet of water for Longmont preparing for future growth.

Today, the City of Longmont produces upwards of 30 million gallons of water per day (during the high-demand summer months), operating two Conventional Filtration Surface Water Treatment Plants (WTP), The Nelson Flanders WTP and the Wade Gaddis WTP. The City also operates an Activated Sludge Wastewater Treatment Facility rated at 14 million gallons per day on average.

Our water originates in the Rocky Mountains as snowmelt. Longs Peak photo: Jason Vallery

Our water originates in the Rocky Mountains primarily as snow. As the snow melts, it runs down the St. Vrain River and is either stored in Ralph Price Reservoir or diverted into pipelines below the Longmont Dam for immediate delivery to the water treatment plants. Additional water originates on the Western Slope from the Colorado River and is delivered via the Colorado-Big Thompson Project through the Alva B. Adams tunnel through Lake Estes and Carter Lake, then down the St. Vrain Supply Canal into our water treatment plants. After the water is treated, it is delivered through transmission pipelines and treated water storage tanks.

For more information on Longmont’s water rights and water supply, please click here.


Cover photo: Longmont Water Wagon, 1900-1920. Courtesy of the Longmont Museum & Cultural Center Archives.