Start with weald. Section of Glauruks. Fish on voralias.

Then planar sanctum water plane.

Then kuo toa tunnel guards.

Then Sahuagin scouts.

You could potentially get someone to lead kiadana stormies to water for you too.

There's also the water mob in high lords.

Plus there's a water room in htos.

There's also an area that fills with water near the aryth, where you kill wights etc.

Ktengs has some water.

Organia has an undead in water.

Trothon has water.

Barovia has water.