The Covid-19 task force on Friday banned street water fights during the Songkran festival for the second year running, on fears it could result in the spreading of Covid-19.
The Songkran festival holiday this year is from April 12-15 inclusive, preceded by a weekend.
Wild street battles with water guns and flinging water from pickup trucks were a normal part of what has been described as the world's biggest water fight, until the pandemic struck.
"Water splashing will not happen this Songkran. We must ask you to cooperate with us," Taweesilp Visanuyothin, spokesman for the Centre for Covid-19 Situation Administration, said on Friday.
He said foam parties would also be banned. The tradition of pouring water over the hands of older people, religious activities and travel between provinces to visit relatives would be allowed.
Thailand has been relatively successful in controlling coronavirus infections, with a new wave of infections in the first two months of the year now levelling off, and recording 90 covid-related fatalities to date .
But strict border controls have decimated the tourism industry, with revenues dropping over 80% as visitor numbers plunged from 40 million visitors in 2019 to 6.7 million last year before the country closed its doors.
A global vaccine rollout has given hope that tourism can be revived and Dr Taweesilp gave more details on Friday on a plan to relax strict quarantine rules starting on April 1.
Mandatory quarantine would be cut from 14 to 10 days for most arrivals and halved for those who were vaccinated, he said.