Having recently retired, Richard D. Boltuck had a bit more time to turn over his water bill and examine how, exactly, his utility had calculated it.

“I thought immediately, ‘This doesn’t make sense,’ ” Boltuck said this week.

He noticed back then, in 2009, something that he — and, he believes, many other residents of Maryland’s Washington suburbs — hadn’t realized. His water and sewer utility, one of the largest in the United States, has had a unique billing system, in place since 1978, that Boltuck believes discriminates against households with three or more people because it can make them pay more per gallon than smaller households. That, he says, violates the Maryland utility law that requires “just and reasonable” rates.

Boltuck, an economist, decided to take on his utility, the Washington Suburban Sanitary Commission (WSSC), by filing a complaint last summer with the Maryland Public Service Commission. The commission doesn’t regulate WSSC’s rates — the Montgomery and Prince George’s county councils approve them with each annual budget — but it hears appeals about utility rates in the state.

What followed is nearly a year of legal research, brief writing and photocopying — all on his own time and dime. Boltuck, who doesn’t have a law degree, estimates that he spends an average of 15 to 20 hours a week on the case and has spent hundreds of dollars in copy fees. (Each brief filing requires 17 or so copies.) Though he lacks legal training, he said his career as an economist left him adept at analyzing documents.

And if, after all this, he wins? Boltuck’s water and sewer bill are likely to go up. As a two-person household in Bethesda, he and his wife are probably  paying below-average rates made up for by the higher rates his larger-household neighbors are paying.

“This is not a matter of self-interest for me,” Boltuck, 61, said after a day-long evidentiary hearing Wednesday before the commission’s chief public utility law judge in Baltimore. “This is something I discovered that seemed very unfair. … Common sense tells you that in larger families, budgets are more stretched with fewer income streams supporting more people.”

Attorneys for the Maryland Office of the People’s Counsel, an independent state agency that represents the interests of utility customers, have sided with Boltuck, calling WSSC’s billing structure “arbitrary and capricious.” WSSC serves nearly 2 million people in Montgomery and Prince George’s counties.

At issue is WSSC’s pricing structure, one that experts say is unique among U.S. utilities. Like many water utilities, WSSC tries to encourage conservation by charging more as customers use more water. But other utilities charge higher prices only for the gallons that bump them into a higher-priced tier. The rest of their water is charged at the lower rates.

WSSC applies the highest-tiered rates retroactively to the entire quarterly bill, back to the first drop. Utility experts say such a system can leave customers with big spikes in their water bill even if they only used a bit more water because the entire quarterly bill got bumped into a higher-priced tier.

Sure, larger households will have higher bills because they use more water, Boltuck says. But they shouldn’t have to pay more per gallon.

WSSC argues that it doesn’t discriminate against larger households because it bills for water based on the daily average amount of water that passes through a meter during a quarterly billing cycle, not the number of people in the home. A single person with a swimming pool and a thirsty lawn could use more water than a home with more people, WSSC says. The utility’s attorneys note that a consultant recently recommended that WSSC keep its rate structure and that most households would have significantly higher water bills if WSSC switched to one flat rate.

The utility says that it recently hired a consultant to examine its rate structure but that making changes would take up to 18 months  due to the utility’s antiquated computer billing system.

Boltuck said he thinks most WSSC customers are unaware of the price differential, which he refers to as “numerical discrimination.” After all, he said, few neighbors compare water bills.

Boltuck is getting help from two Maryland residents who learned of his fight against WSSC. Sue LaCourse, 54, a substitute preschool teacher who lives in Laurel, and Peter Karpoff, 72, a retired U.S. Department of Energy economist who lives in Silver Spring, are helping him with ideas and circulating a petition to change WSSC’s rate structure.

At the evidentiary hearing this week, Boltuck looked like just another lawyer in a conservative gray suit and tie. As a “pro se” party to the case — someone who’s representing himself, without a lawyer — he had to ask the judge about which documents he could submit as evidence, and the judge had to guide him a few times about what kinds of questions he was allowed to ask.

But  mostly, Boltuck sounded like a lawyer who had meticulously researched his case and tried to pick apart the testimony of the other side’s witnesses. One of WSSC’s attorneys even complimented him after the hearing. (Pro se litigants are notorious among lawyers for turning legal proceedings into drawn-out circus sideshows.)

“I think it’s wrong, and this is something I can do,” Boltuck said after the hearing. “I didn’t know what I was doing up there today, but I can look at documents and write testimony.”

The utility judge’s decision is expected by Sept. 9. Before then, Boltuck has another legal brief to file.