(CBS) — Rain barrels have become popular in the Chicago area to save money on water bills when watering lawns and gardens but an expert warns that, if not installed properly or taken care of, could become mosquito breeding grounds.

Last year, the Metropolitan Water Reclamation District says it distributed more than 29,000 rain barrels to Chicago area homeowners.

David Zazra of the North Shore Mosquito Abatement District says those rain barrels have proper screening to prevent adult mosquitoes from getting in to lay eggs. But, he says, even with those barrels, it’s good to put inside a mosquito larva control product that are available at hardware stores and home center stores.

Zazra says the product is, “a naturally occurring bacteria and what happens is that crystals form and mosquito larvae feed on these crystals from the bacteria, it ends up destroying their digestive system and they don’t emerge as adults.”

Zazra also says you should remove any excess water that pools on top of the rain barrel and regularly check for leaks and cracks that could allow mosquitoes in.

Homemade rain barrels, especially, can be a place for mosquitoes to develop. Zazra says some people just take old trash cans and allow rain water to collect in them. He says those barrels need to have good enough screening to prevent adult mosquitoes from getting inside to lay eggs. He says, “They breed mosquitoes by the tens of thousands.”