Water Life
Gundul

new mobs for your river and sea water

Sounds
AntumDeluge

A set of free sounds & API.

Placeable Buckets for Catching Rainwater
Noodlemire

Allows empty buckets to be placed as nodes in order to collect rainwater.

Climate API
TestificateMods

A powerful engine for weather presets and visual effects. Requires a weather pack like Regional Weather.