Virginia Tech researchers who exposed the lead problem in Flint, Michigan, say the city's water quality has greatly improved, based on tests at 162 homes.

Researchers reported Thursday that 45 percent of homes tested in July showed no detectable levels of lead. The head of the team, Marc Edwards, says the situation is "dramatically better" than last year when he sounded the alarm over lead, due to a lack of corrosion controls.

Edwards says Flint residents should continue to keep filters on their kitchen taps or use bottled water until officials say unfiltered water is OK to drink.

Flint's water was contaminated when the city began using the Flint River for its supply in 2014 without adding chemicals to control pipe corrosion. Protective coatings in old pipes eroded, releasing lead.