LAKE CHAPLAIN — Mark Weeks remembers when he first came to work in 1987 at the city of Everett’s water filtration plant.

“When I first got here everything was analog,” he said. “It was all switches and paper recorders.”

Weeks now is the manager of the plant, at the south end of Lake Chaplain. And the plant now is controlled mostly by computers, with switches and levers replaced by mice and touchscreens.

Yet the 33-year-old plant has its shortcomings. Eight of the approximately 20 staff who work on site are in the maintenance business. One of the two backup generators, which would kick in if the main electric line were to go down, is out of service, meaning there’s a rental in place.

Add to that another concern on the horizon: growth.

The city’s system supplies most of Snohomish County with water for drinking and fire protection, about 600,000 customers total. According to Snohomish County, the population is expected to grow by another 200,000 people over the next two decades, a 26 percent increase.

The plant has a capacity of 134 million gallons per day, which represents a peak flow under good conditions, said John McClellan, the operations superintendent for Everett Public Works.

That flow likely couldn’t be sustained over an extended period, he said.

The typical daily production from the plant is 50 million gallons of water, but during the drought in the summer of 2015, nearly 100 million gallons were sent through nearly every day.

One way of planning for expected growth is a pilot project to test whether the capacity of the plant’s filters could be increased. Squeezing a bit more capacity out of the filters could save tens of millions of dollars over the long run, McClellan said.

The main source of the city’s water is Spada Lake, with Lake Chaplain as a secondary source. Chaplain also is the site of the filtration plant and the starting point of the pipelines that carry fresh water to the city’s reservoirs.

The state Department of Health caps the production of each of the plant’s eight filters at a rate of 8 gallons per minute for each square foot of filter.

As part of the pilot project, there is a room with a smaller version of a filtration plan with three filters identical in composition to the plant’s main filters: cylinders filled with 52 inches of anthracite coal atop a gravel base and a porous clay block.

Once the pilot study begins, possibly in November, Weeks and his staff will run water through the filters at higher rates. A moderate increase from 8 to 10 gallons per minute per square foot could lead to big savings.

After about a year, the results will be submitted to the health department for approval.

“We have to be able to produce the same levels of turbidity,” Weeks said, referring to naturally occurring particles suspended in the water. “If you can increase your production capacity, then you don’t need to build treatment basins.”

A new set of four filter systems could cost as much as $60 million, he said. Instead, running the existing filters at a higher capacity would mean installing new inflow pipes, at a more moderate cost of up to $3 million.

What that means downstream is significant. The filtration plant’s capacity of 134 million gallons per day could be increased to about 165 million.

If hotter and drier weather becomes common, a higher capacity plant, coupled with conservation measures at the tap, could help manage the increased demand.

Last year’s drought triggered water-use advisories for the first time since 2001. The advisories asked water customers to cut their use by 10 percent to maintain enough water in Spada Lake.

Spada Lake was only about 68 percent of its normal capacity at the time, and the advisory wasn’t lifted until November. It wasn’t until later that month that the water level returned to normal.

The summer of 2016 has been a lot wetter.

“We are pretty much topped off,” McClellan said.

Chris Winters: 425-374-4165; cwinters@heraldnet.com. Twitter: @Chris_At_Herald.