The culprit, however, turned out to be new homes combined with hot showers, reported local newspaper Skånskan.
Tests of the initial suspect, the drinking water, were taken from several homes in the area. Copper levels were tested, as the metal is known to dye hair green.
When the tests showed normal copper levels in the water delivered to houses, engineers were confounded.
However, left overnight, the copper suddenly skyrocketed to five or ten times the normal amount.
Hot water left overnight peeled copper from the pipes and water heaters, and into the water.
The problems were most severe in new houses, where pipes lacked coatings.
"The samples we took from older houses have lower copper levels," said environmental engineer Johan Pettersson, to local newspaper Skånskan.
Inhabitants in the area who wish to avoid an involuntary dye must now wash their hair in cold water.
Or move to an older house.