Consumption of soda and other sugary drinks fell by more than a fifth in low-income neighborhoods of Berkeley after the California city became the first in the U.S. to introduce a special tax last year, according to a study published Tuesday.

The peer-reviewed research is the first to measure the impact of the penny-per-ounce tax. It found that consumption declined 21% and many residents switched to water after the tax went into effect in March 2015, according to the study published online in the American Journal of Public Health.