You would think the hardest part of Twila Singh's job is spending hot summer days around swimming pools and resisting the urge to jump in. But Singh has more important tasks.

As an environmentalist for Hennepin County's Human Services and Public Health Department, she is on a team of about 20 inspectors doing safety checks throughout the county at 43 beaches and 483 pools, including all indoor and outdoor pools and spas except those owned by individuals. They inspect each place when it opens for the year and again later in the summer.

On Wednesday, Singh and Joseph Jurusik, a supervising environmentalist for the county, demonstrated inspection procedures at the Christmas Lake Manor apartments in Excelsior. Singh showed how they test samples of water for pH balance — the measure of the water's acidity or alkalinity — which, if too high, can be uncomfortable or cause injury.

They check for chlorine content, an even bigger deal because too much chlorine can burn the skin and too little can allow growth of bacteria, potentially causing infections or disease.

The issue of pool-borne illness made news last week when the U.S. Centers for Disease Control and Prevention (CDC) reported that outbreaks of "crypto," short for the parasite cryptosporidiosis, have been increasing by 13% a year. Between 2009 and 2017, public health officials from 40 states and Puerto Rico reported 7,465 cases of crypto, with 287 hospitalizations and one death.

The illness, which causes watery diarrhea for up to several weeks, can be transmitted by swallowing water in swimming pools. It can be dangerous for children, pregnant women and people whose immune systems are compromised.

People should not enter swimming pools if they have diarrhea or recently had it. But Singh and Jurusik said the report isn't cause for alarm since outbreaks of illness from swimming pools are rare.

Pools must be functioning properly and stocked with lifesaving equipment such as long hooks and life-ring buoys. Surrounding walkways must be free of hazards, fences must be the proper height, and gates must close and latch on their own to keep out stray children or animals.

Rules and safety information must be posted, such as the sign at Christmas Lake Manor that reads "WARNING: No lifeguard on duty," and prohibits use of the pool by anyone under 18 not accompanied by an adult.

The rule might seem strict, since many lifeguards themselves are under 18, but it suggests that teenagers left on their own can get into hijinks.

"Not just that they could. That they would," Singh said, laughing.

Any pool that doesn't pass inspection must close, but the fixes are made and pools usually reopen within hours or a day or two, Jurusik said.

"Pool operators are generally very good people and they're really conscientious," he said. "Especially when they've got kids pressing up against the fence waiting to get in."