The bug
Gardens on hills have exposed water that washes away crops. Due to MC-140619, the water initially is still, but once a nearby crop grows, the water is updated and flows out onto the farm. Ideally, water blocks shouldn't generate unless there are blocks all around them.
How to reproduce
Last checked in 20w10a
Even if these seeds and coordinates do not show this problem anymore, it might not be fixed, instead maybe the world generation just changed.
Seed: 4878702018839826212
/execute in minecraft:overworld run tp @s -9965.14 68.89 2093401.44 -336.83 34.20
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I don't think this is part of village generation, just a waterfall
I don't believe so, this can occur when the slope is only decreasing by one block and occurs often in village gardens.
I've added some pictures of the water before it actually stats flowing that show more examples of the generation on slopes and the relation to MC-140619.

Affects 19w08b
Hi there!
Can confirm for 1.16.1 and 20w27a.
Can confirm in 21w05b.
Can confirm in 21w06a.
Can confirm in 1.17.
The problem is the water source that is not always surrounded by other blocks/dirt, so it can flow away. Usually it doesn't flow when creating a new world for some reason, which for itself is a bug.