Imagine Joseph Pomares’s surprise when he went to his local post office in Long Island City, Queens, one Saturday last summer to collect a certified letter. He had no idea what awaited him, but the last thing he expected to find was a summons from the city’s health department.

The summons referred to a two-story brick house in Astoria that Mr. Pomares, a 53-year-old home renovation contractor, had recently refurbished and rented to tenants. Titled “vector control inspection work order,” the citation accused him of violating what appeared to be a paradoxical imperative: “standing water” in a birdbath. The violation of Article 151 of the city’s health code could subject him to a $2,000 fine.

“I bought the birdbath brand new. I thought I was doing something good, and I changed the water every other day,” Mr. Pomares recalled. “I had beautiful birds.”

Mr. Pomares was one of 699 New Yorkers who learned last year that April showers can bring a lot more than May flowers. They can also deliver property owners a summons. Most of those issued in 2011 were for poorly maintained swimming pools and standing water at construction sites. Even an ordinary puddle can lead to a violation. So can a birdbath, as four surprised New Yorkers found out.