A video clip of a fourth water-bucket drenching of uniformed NYPD officers emerged on Thursday, as the head of the sergeants’ union called for the ouster of Commissioner James O’Neill.

The 15-second clip — bearing a watermark of the @harlem4real Instagram account — opens with a boy who appears to be in his teens creeping up behind a cop and emptying a green bucket of water over his head.

That ambush is quickly joined in on by another two youths — one of whom looks to be no more than 6 or 7 — splashing the lawman as his partner looks on.

After a cut, two youths are seen soaking a cop in the same location, before another blasts a second cop with a green, yellow and white plastic water gun at point-blank range.

That officer is seen feebly raising his arms in protest, and at no point are the officers seen engaging or chiding the youths.

The video appears to have been taken in a park, but it wasn’t immediately clear exactly where or when it was shot.

The clip was tweeted out by the Sergeants Benevolent Association on Thursday, captioned with a blistering rebuke of top cop O’Neill for letting the aqua onslaughts play out on his watch.

“NYPD has surrendered under O’KNEEL -ANOTHER WATER TOSSING VIDEO,” reads the fiery tweet, adding a message to the Finest. “No more MEMO’s– DEFEND YOURSELF before YOU get seriously injured or KILLED.”

The tweet offered a dire warning that, while the water attacks appear innocent, they could just as easily be deadly.

“These buckets can contain ACID, BLEACH or other CHEMICALS,” reads the tweet, before closing with another call for O’Neill to get the boot. “O’KNEEL MUST GO, take the CLOWNS with you! No CONFIDENCE.”

This on-video soaking is the fourth to emerge within a week, following one in Brooklyn and a prior Harlem attack, plus a third in the Bronx.

Three men, including a reputed Crips gangbanger, have been arrested in connection with the first two incidents.