The move came after people flocked to the street on Wednesday evening for water fights in defiance of the ban.
The water battles continued until 11pm, prompting the Bangkok Metropolitan Administration (BMA) to alert police over fears of a new Covid-19 outbreak.
Officers from the Tourist Police Bureau and Chana Songkhram Station quickly set up checkpoints at both ends of the street in Phra Nakhon district.
A ban on water splashing has been imposed nationwide by the Centre for Covid-19 Situation Administration (CCSA) amid fears of a surge in infections over Songkran.
Also banned in Songkran activity areas are face powder daubing, foam parties or similar activities, and sale or consumption of alcohol.
Metropolitan Police chief Samran Nuanma visited the checkpoints on Thursday and said that police had charged eight owners of Khaosan restaurants for violating Covid-19 restrictions, including by allowing people to splash water.
“Since the checkpoints were set up this evening, there have been no more reports of anyone violating the no-splashing rule,” he said.
“Some people had carried water guns onto Khaosan Road, which is also prohibited.”
He said that police would prevent people carrying water guns from entering the road and confiscate any water guns found on Khaosan.
Samran added that police officers would man checkpoints at the entrance and exit of the road until the end of the Songkran festival on Sunday (April 17).