Watering may be obtained from Gathering within the Forever Fields. It is used to gather water 
and to increase the growing time of any planted seeds by 50. This effect also stacks with the farming potion.
Watering can initially only waters the first patch (from the left) and may be slotted with gems to water more patches (+1 patch per gem slotted).
It is hinted that rain water collected may depend on the weather, but currently there is no option to know the weather in Idle Pixel.