Some would argue that to be safe you should compost it. I would say that with well raised ducks and non-stagnant water you should be fine. I have used water from a teeny little duck pond on food plants with no ill effects. I would maybe avoid putting it on things like salad greens you will harvest very soon, other things to be eaten raw, etc. But plants do love it, and I tend not to worry about the manure, especially watered down.
We used duck manure mixed with bedding on our squash and tomatoe plants, and it seemed like it was the best kind of manure. We have also watered our berries, trees, and garden with their pool water, and it seems fine.
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