In Rosemount, city officials have strict advice about saving water: “DON’T overwater your lawn” and “DO let your lawn go dormant under drought conditions.”

But the city itself last year installed a splash pad in one of its parks that spit out 5 million gallons in its first summer — and expects that figure to rise this year.

Safer, cheaper, more active and engaging than wading pools, splash pads are being touted as the nation’s hottest new parks amenity. And they are proliferating here.

Woodbury and Burnsville added new ones this summer, as did Minneapolis. Maple Grove’s is coming soon, and Columbia Heights is building one slated for 2016.

Minnetrista last week approved a plan that includes one. Hugo takes up the question in September, and Savage is eyeing one too.

But splash pads run through torrents of water at a time when hydrologists warn that we’re depleting the clean, pure aquifers far beneath the soil.

Thomas Schaffer, president of locally based USAquatics, which has done $800 million worth of aquatics projects in more than 30 states, is worried.

“We probably do 80 percent of municipal pools in Minnesota,” he said, “but we get less than 10 percent of the splash pad contracts, because 9 of 10 are running off the potable water system and it all goes into sewers.

“And that is a waste. That is not sustainable. We don’t do ’em that way. We just say ‘No.’ The only type we do is recirculating,” most recently in 2013 in Eden Prairie.

The steep drop in water levels at White Bear Lake from 2006 to 2013 drew attention to an issue that is largely hidden from public view. Even today, there’s extra sensitivity around plans for a splash pad in nearby Hugo, where the increased use of water was blamed in part for the dramatic loss.

“That connection is a lot harder to make than a lot of people realize,” said Hugo City Administrator Bryan Bear. “But our City Council has made it a priority to be responsible stewards of the aquifer.”

A recirculating system could be an answer for Hugo, he said, or perhaps re-use of water to irrigate lawns.

But he’s impressed by what he hears from cities like Cottage Grove, which “has a great story to tell about budget impacts and parks attendance.”

Popular — and cheaper

There’s the rub: While pools are dangerous enough to require entire staffs of attendants such as lifeguards, splash pads scarcely need a single overseer.

Parents and kids are drawn to the misters, the sporadic dumpers, the jets and columns of cold water leaping in sudden bursts from the ground.

On a hot weekday morning last week, Cottage Grove’s Highlands Park was largely empty — ball fields, tennis courts, even its shaded playground. But the splash pad, opened in 2012 to replace an aging pool, was alive with kids.

“We were heavily subsidizing that pool,” said Parks Chief Zac Dockter. “For every person who paid the $2 fee, the city was chipping in $12 to $14. And use was declining. Today we have more than 23,000 people coming each summer, and it costs us maybe $5,000 in staffing per summer to have someone swing by quickly to clean up once a day, versus $100,000 for the pool.

“We do lose water, 4 million gallons a summer versus 1.5 for the pool. But that’s still less than 1 percent of the city’s total use.”

Risk for deep aquifers

Dockter and his counterparts in Burnsville assert that they’re not just throwing water away — it returns to nature.

Water used at a newly opened splash pad at Cliff Fen Park “drains into a nearby drainage ditch and percolates back into the groundwater to replenish the natural water table,” said Garrett Beck, recreation and facility manager.

But hydrologists say that the shallow water table is not the same as the much deeper aquifers from which cities prefer to draw drinking water.

Shakopee sinks one of its 18 wells 800 feet deep, almost exactly as far down as the IDS Tower is tall. Waiting for water to sink that far, while you’re pulling it out far faster, is a losing proposition, critics say.

“If you are taking potable drinking water and infiltrating it in that way,” said Darrell Gerber, research and policy chief for the Freshwater Society, “that does kind of smack of being wasteful.”

Not all cities installing splash pads are pulling water out of deep aquifers. Columbia Heights, for instance, and both Minneapolis and St. Paul use water from the Mississippi River.

Some cities using well water are trying to conserve by reusing splash pad water to irrigate ball fields and the like. Woodbury Parks Director Bob Klatt said his city does that, and Rosemount is considering doing the same, said Parks Director Dan Schultz.

“We hope that in the future we might reuse some of the water in a pond, pumping out of that for irrigation,” Schultz said. “We haven’t been up and running long enough to know if it’s feasible. With evaporation, absorption, is there enough to pump out?”

Hydrologists and conservation advocates stress that not even recirculating systems, which constantly reuse the same water, can totally conserve it.

“You can’t keep reusing the same water endlessly,” said Joe Richter, hydrologist with the Minnesota Department of Natural Resources. “Eventually the water gets so dirty, so full of chlorine, that it has to be dumped and fresh water takes its place.

“Water evaporates, but stuff in the water doesn’t; there’s a constant need for fresh water, though it’s better than using fresh water every time.”

‘A tough change’

A major challenge for the Twin Cities, many agree, is getting across the point that even though the whole region seems abundant with water, in reality groundwater supplies are not infinite.

“The metro area has enough water in the short-term,” the Metropolitan Council warns in a draft report being considered this month, “but long-term projections predict potentially significant impacts to aquifers if water continues to be consumed at current or higher rates and using current sources.”

The worst pinch point, the report adds, is summer. Water use spikes, and the public winds up spending a fortune to install infrastructure that isn’t used at other times of year.

The Freshwater Society is updating a 2013 report on water use, Gerber said, “and [in] talking to lots of experts in agencies, what comes up over and over again is a real concern over whether we’re ready to reach the point where we can’t assume any longer that there’s more than enough water. People are not going to be prepared. It will be a tough change.”

In the meantime, he said, “the challenge for cities is so many factors to keep in mind: trying to find something that works for kids with access limitations, watching out for liability and safety — but it’s also making sure we’re thinking about not allowing the assumption that there’s plenty of water [which would] prevent the best use of that resource.”