The singer took to Twitter on Saturday (August 4) to share her new drinking habits in the wake of the birth of her daughter Maxwell.
"Responsibility has drastically changed my life!" she posted. "Saturday night drink of choice.... WATER! :)"
The 32-year-old previously admitted to Elle magazine that she had trouble giving up alcohol during her pregnancy.
"I'm a free-spirited girl, but giving up my scotch? My Macallan 18? That was hard for me!" she said.
Simpson is currently attempting to lose the 70lbs of extra weight she gained during her pregnancy.