When it comes to storing water, Denver’s picturesque mountain reservoirs get all the glory.

Less visible, but just as important, are the 30 underground storage tanks in 18 locations around the metro area, each storing anywhere from 2.5 million to 25 million gallons of water, delivered from one of Denver Water’s three drinking water treatment plants.

In 2011, Denver Water embarked on a decade-long transformation project that began with the expansion of the Lone Tree underground storage site. Three projects later, those efforts will culminate in 2020 when we complete a $100-million overhaul of the Hillcrest water storage facility in southeast Denver.

Hillcrest was born in the late 1950s and early 1960s, when Denver Water built a state-of-the-art storage and pumping facility to replace several small, temporary pumping stations.

Much has changed in 50-plus years, and with increased water demands from the ever-booming Denver metro area, particularly southeast of town, it was time for a makeover.

Since early-2016, Denver Water has worked to replace Hillcrest’s two existing 15-million-gallon rectangular storage tanks with three 15-million-gallon, circular, “post-tensioned” concrete tanks.

“Post-tensioned” is a fancy way of saying the new tanks are more durable and watertight, said Martin Garcia, Denver Water senior engineer.

“That’s a good thing for everyone — particularly customers in the southeast Denver area,” he said. “Hillcrest is really the nexus of our distribution system, and the added storage capacity will reduce strain created by the area’s growing population, allowing us to keep the water flowing well into the future.”

The new tanks will sit slightly south of the existing tanks and will be buried up to their roofs, which will be visible.

In addition to the new tanks, the Hillcrest pumping station — one of 22 in the Denver Water distribution system — is getting its own upgrade.

Beyond Hillcrest, Denver Water plans to spend $1.25 billion on 143 capital improvement projects throughout the water system over the next five years.

Those projects include a $400 million state-of-the-art water treatment plant north of Golden, upgrades to the dam at Ralston Reservoir and replacement of a major water delivery pipeline in Jefferson County.