The city of Flint in Michigan declared a state of emergency after high levels of lead were detected in the blood of local children. A new study has linked the elevated blood lead levels with the city's drinking water system.

A research conducted by Dr Mona Hanna-Attisha found the rise of blood lead levels in children who drank Flint River water as long as 17 months, MLive reported.

The research published by The American Journal of Public Health found that areas in Flint with the highest levels of lead in tap water corresponded with the areas where young children with the highest blood lead levels lived.

The new study also confirmed the earlier research in September that found the blood lead levels in children had at least doubled after the city began using water from the nearby Flint River in 2014.

According to LiveScience, Flint changed its water source from Detroit's water supply to Flint River in 2014. The city planned to use Flint River system until 2016 to save million dollars, so the state could construct a new pipeline connecting Flint to Lake Huron in Detroit.

But the water from Flint River wasn't properly treated and had absorbed lead from the pipes. While Detroit's water was treated with anti-corrosive chemicals to keep the lead from leaching.

A number of Flint's residents have filed a lawsuit against the state, the city, and several officials for exposing their families to highly toxic drinking water.

In Science Alert, the lawsuit said that the state and local government officials ignored irrefutable evidence that the water pumped from the Flint River exposed city residents to extreme toxicity for more than 18 months. The lawsuit also mentions hair loss and skin lesions as effects reported by the exposed residents.

WHO said that the lead exposure to children affects their brain development resulting in reduced Intelligence Quotient (IQ), behavioural changes such as shortening of attention span and increased antisocial behaviour. The lead poisoning in children also reduces educational attainment.

The City of Flint now advises children, the elderly, pregnant women, and anyone with a weakened immune system to seek advice from their doctor about whether they should be drinking the water.

In October, Flint has switched the main water supply back to Detroit water system. Michigan governor has financed millions dollar to the water system switchback.

After a state of emergency declared, the Federal Emergency Management Agency (FEMA) has sent 28,000 litres of bottled water to a local food bank. The city is now offering the residents free water testing and free water filters.

However, there could be some areas in the city where the water is still unsafe to drink if left unfiltered even now.