Workers at the Fresenius Medical Care clinic in West Columbia discovered the contaminated water before anyone was hurt. A monthlong investigation led deputies to Donald Foster III, who has been charged with attempted murder and second-degree burglary.

Foster was suspended from his job as an equipment technician and patient care technician on July 2, but he came back less than a week later and tainted the water, police said.

“He had planned to carry out a mass murder in order to get back at his employer,” Lexington County Sheriff James Metts said.

Foster poured bleach into tanks that hold the purified water used to filter waste from the bodies of 20 patients, hoping the deaths from his sabotage would bankrupt the firm, police said.

His bond was set Thursday at $525,000, and he remained in jail. The 49-year-old single parent asked a judge to let him out of jail because he needs to take care of his 5-year-old daughter.

“This is all a misunderstanding, really,” Foster said, speaking from behind a mesh-covered opening behind a locked door.

Foster’s lawyer asked for a reasonable bond, and declined to talk about the case after the hearing. Authorities asked for as high of a bond as possible, but did not give a specific amount. They said Foster was a flight risk with no regard for the lives of other people.

Foster faces up to 45 years in prison if convicted of both charges.

Foster was suspended because he was trying to get elderly patients to give him their prescription painkillers, Metts said. He sneaked past a cleaning lady on a Saturday and poured bleach into the tanks that hold the purified water for the dialysis treatment, knowing that any contaminant could kill people whose kidneys are already so weak they filter very little of the impurities in their blood, authorities said.

Pure water is so critical to the dialysis process that workers check the tanks several times a day, including before any patients are hooked up to the machines, said Jon Stone, a spokesman for German-based Fresenius Medical Care.

“Although patients’ treatments were slightly delayed, no one was harmed and all of our patients received their scheduled treatments that day. We are proud of our staff and are grateful that they caught this situation,” Stone said in a statement.

The workers called police after discovering the contaminated water. Foster was fired, and representatives of the clinic who were at his bond hearing again asked he be kept far away from the facility. They did not give their names.

The sheriff said Foster denied the sabotage at first, but as detectives gathered more evidence, his story became less credible.

“He finally did admit he had done it,” Metts said.

The indifference Foster showed toward human life and the very patients he made sure were comfortable as they endured dialysis treatments for several hours, several times a week shocked the sheriff.

“He had no empathy or feeling for human life at all,” Metts said. “All he wanted to do was destroy this company.”