The explosion occurred at 1:30 am at the water-pumping station, police said.
They said security camera footage in the area showed two men arriving at the station on a motorcycle.
The footage showed one man getting off the back of the motorcycle and carrying a metal paint can into the station.
The explosion occurred while he was placing the can inside the station, police said. The man was identified as Nud Tanilo, 26, a resident of Tambon Rusoh in Narathiwat’s Rusoh district.
Once the bomb exploded, the motorcycle driver raced from the scene, police said.
Police said the suspect’s left arm was broken and his face was severely burned by the explosion.
He was rushed to the Yala hospital where he remains in critical condition, police said.
Police said they suspect the pair wanted to damage the main water pumps of the station but the bomb accidentally exploded before it was installed.
At 8 am on Sunday, a team of bomb disposal and forensic science police examined the scene with soldiers.
Based on fragments of the bomb, the team estimated that it carried between five and 10 kilogrammes of gunpowder. Police said the goal was to detonate it remotely, but the plan failed.