No underwater bullets (CWaterBullet)

[MyGamepedia]

CBaseEntity::HandleShotImpactingWater creates water bullets IF CBaseEntity::ShouldDrawUnderwaterBulletBubbles returned TRUE. The second method never returns true in mp because it checks if MaxClients == 1 and also uses UTIL_GetLocalPlayer().
You can check in bm_c2a5a when npc_apache shoots at water to hit you.
Not offsets, but CBaseEntity::HandleShotImpactingWater also can be find by strings: "gunshotsplash", "waterbullet", "TracerSound". It also calls CBaseEntity::ShouldDrawUnderwaterBulletBubbles directly.

[MyGamepedia]

Also true for Valve games.

[MyGamepedia]

it looks like in our case we should always return true no matter what