Water under Level 4 will turn into Mushrooms if you don't merge.
You can also obtain Puddles of Water from the Wise Elder by both tapping and harvesting.
When merging high-level Wisdom trees, you may receive Rainforest as a byproduct. Rainforest produce Clouds which will rain Puddles of Water, if open land is available.
Ponds Level 5 and above can be harvested for Seaweed.
The Mirror of Sky produces frequently - perhaps every 1-2 hours, that you can tap up to 20 times a production. Tap outputs include Score Props level 6 and 7, Piles of Wealth, Ugly Fish eggs and nests, and Medium Treasure. You can also harvest for Seaweed.
Starting at level 7 and above pond needs 4 squares in your camp.