The Bug:

Turtle shell helmets don't apply the water breathing effect to non-player entities.

Steps to Reproduce:

1. Summon a zombie in some water that is wearing a turtle shell helmet by using the command provided below.

   /summon minecraft:zombie ~ ~ ~ {ArmorItems:[{},{},{},{id:"minecraft:turtle_helmet",Count:1b}]}

2. Wait around one minute and watch it closely.
3. Take note as to whether or not turtle shell helmets apply the water breathing effect to non-player entities.

Observed Behavior:

Turtle shell helmets don't apply the water breathing effect to non-player entities.

Expected Behavior:

Turtle shell helmets would apply the water breathing effect to non-player entities.