Flashing lights in the water supply in Flint, Michigan, has drawn the ire of the public and local officials, but some still have no clue of what caused the contamination of drinking water in the city of Flint.

The Associated Press has more:The Associated American Medical Association said on Wednesday that it had diagnosed a dozen children who were poisoned and at least nine adults who have died as a result of the tainted water.

The hospital where the children were taken, Children’s Hospital of Michigan, said in a statement that it was treating six children and two adults with suspected poisoning.

The Associated Press also reported that a Flint resident has died of a rare form of kidney cancer.

Officials say the Flint drinking-water problem was caused by an unhygienic lead plumbing system that was improperly installed, causing a buildup of lead in the pipes that carry water to homes and businesses in the Flint area.

The city began replacing aging pipes in April.