(CNN) Residents and officials in Newark, New Jersey, are trying to determine exactly when lead began leaching into the water supply.

It's a vital question, since lead contamination in water can damage a child's health. Even low levels of lead have been linked to serious, irreversible damage to developing brains. For this reason, experts say that there is no safe level of lead in drinking water.

The local government in New Jersey's largest city has begun to address the unsafe level of lead in water supplied to some residents, but still struggles to answer when -- and how -- this began.

Generally, city officials say the elevated levels of lead in Newark's drinking water are "due to the releasing of lead from plumbing and lead service lines on private property between the street and approximately 15,000 homes." Also, the Pequannock water treatment plant's corrosion control system "became less effective at reducing the corrosion of lead pipes and resulted in rising lead levels in some homes with lead service lines throughout Newark," the city said.

The long-term fix involves replacing service lines, but until that multi-year project can be completed, Newark is implementing short-term solutions.