
Among the seven men and seven women, five were severely injured, police said.
The accident happened shortly before noon on a road along an irrigation canal in Tambon Ban Mae Pong.
The bus driver, Suthat Kongngern, 36, told police that he had been taking the tourists from a resort to visit the San Kamphaeng hot springs but the brake system malfunctioned at a curve in the road. The bus then fell into the canal and flipped over.
Suthat claimed he was only driving 30 kilometres per hour.
Police have charged him with reckless driving causing injuries.