ONWR warns of summer storm from April 28 as national water storage drops to 60%

Thailand’s Office of the National Water Resources (ONWR) has warned the public to prepare for a new round of summer storms from April 28 to May 1, 2026, as the latest nationwide water situation shows overall reservoir storage at 60%, with several key areas still requiring close monitoring.

In its update issued at 7.00am on April 26, 2026, ONWR said upper Thailand is expected to face another summer storm wave towards the end of the month, while overall reservoir levels remain in the “monitoring” range—particularly in the Central and Eastern regions, where water volumes have started to decline.

ONWR noted that rainfall across upper Thailand was easing on April 26, but thundershowers and gusty winds could still occur in some areas, with the North facing a higher risk of heavy rain in certain locations.

Summer storm outlook: April 28-May 1

ONWR said the summer storms are expected to bring thunderstorms, strong winds, and possible hail in some areas, with impacts likely to develop in phases:

• First affected: the Northeast, North and East
• Next phase: the Central region, including Bangkok and surrounding provinces

National reservoir levels (as of April 26, 2026)

ONWR reported total nationwide storage of 48,530 million cubic metres (60%), with usable water at 24,431 million cubic metres (43%).

By region:

• West: 19,342 million cu m (68%) – highest
• South: 5,033 million cu m (64%)
• North: 16,523 million cu m (60%)
• Northeast: 5,802 million cu m (48%)
• East: 1,128 million cu m (37%)
• Central: 702 million cu m (36%) – lowest

Four key dams in the Chao Phraya basin

For the Chao Phraya basin, ONWR reported:

• Bhumibol Dam: 8,373 million cu m (62%)
• Sirikit Dam: 5,754 million cu m (61%)
• Kwae Noi Bamrung Dan Dam: 320 million cu m (34%)
• Pa Sak Jolasid Dam: 233 million cu m (24%)

EEC reservoirs and water quality

In the EEC area, ONWR said three main reservoirs were steady:

• Prasae Dam: 59%
• Bang Phra Dam: 50%
• Nong Pla Lai Dam: 48%

On water quality (salinity):

• Tap water supply (consumption): the Chao Phraya River at the Samlae pumping station remained within standards (not exceeding 0.25g/litre)
• Agriculture: the Tha Chin, Mae Klong and Bang Pakong rivers were within normal standards (not exceeding 2g/litre)

ONWR advised people in storm-risk areas to check the stability of buildings and structures, and avoid open spaces, large trees and unstable billboards from April 28 onwards.