As of this writing, the Philippines has just produced evidence that its coast guard and resupply vessels were subjected to assault by water cannons from China Coast Guard ships on 5 August 2023. This occurred during the regular rotation and resupply mission to the Philippine Navy's outpost aboard the grounded BRP Sierra Madre at Second Thomas (Ayungin) Shoal, and is reminiscent of a similar incident in November 2021.

A water cannon is generally considered an anti-personnel, non-lethal weapon, used to stop, discourage or punish an unwanted activity. The tactic consists of blasting another ship with a high-pressure water stream. It is a mainstay in South China Sea incidents, as it is one of very few ways ships at sea can kinetically attack other vessels in a way that is unlikely to cause severe damage to materiel or personnel.

Even so, it is not hard to see how its use against a very small vessel like this one could turn catastrophic: 

Other examples: 

On June 7, 2015, a Chinese vessel chased down and blasted a Vietnamese fishing vessel with its water cannon about four to five nautical miles from Bombay Reef. One of the Vietnamese crewmen broke his leg during the altercation.

The May-July 2014 Haiyang Shiyou 981 Oil rig standoff saw numerous instances of water-cannoning. In one incident reported by Vietnamese state media, at 11:30 am on June 1, 2014, Vietnamese fisheries surveillance ship KN-635 was put under a sustained hosing barrage by a Chinese vessel. Two other Chinese ships (CCG 46001 and 46105) employing blocking, ramming, and water cannoning tactics prevented Vietnam Coast Guard cutter CSB 2016 from supporting the beleaguered KN-635.

CCG 46105 hosing and then ramming Vietnam Coast Guard cutter CSB 2016, June 1, 2014 (Source:  VNA via Thanh Niên)

On 27 January, 2014, a CCG vessel employed its water cannon to force Filipino fishermen out of waters near Scarborough Shoal. The Philippine government did not provide further details.

See the rest of the playbook here.