Not to cast aspersions on your ducks and their health, but I would be VERY reluctant to spray any animal or bird poopy water directly on anything I was going to eat. Using it as ground watering/drench would be much more to my liking. Using it in the late season, on fruit trees that have been picked, might be OK, but since any bacteria or fungus that landed on the fruit any earlier would be able, given the right growing conditions, to keep on growing, I wouldn't do it. The latest E. coli on spinach scare, to the best of my recollection, came from the run off from a feed lot (which, I grant, has other practices that you don't observe, but even so...) running into a spinach field and splashing onto leaves, so the use of animal wastes straight or diluted with water is probably not a good idea. Using it in the off season, maybe OK, as anything bad that grew might be gone by the time you ate the results. A careful ground drench or using it on ornamentals would be fine, IMHO.

Is it because the water tastes funny? After the kids were in it.. (lotions, soaps, etc) or do you think they are just frightened? If its the first you can change some of the water if its the 2nd they will go back in after they realize that its quiet and ok to go back in.

Ya, although it sounds like a great idea, a few duck can easily take out all your plants in a short while. Their diet would have to be substituted with grains and such, otherwise your going to be throwing in more plants into that pond than you can handle. The thing with most aquatic plants is that unless you give the pond a few years to let the plants grow, they are going to be far and wide if you throw some dabbling species of ducks in there. If your client doesnt intend on eating these ducks or hand feeding them bread and such, get some diving ducks and stock the pond with fish. Also another plant not mentioned was wild rice. Other than the plants mentioned, your really getting yourself into a big project. I would talk to an expert on ducks, or try to find an ecologist.

Kendra, the ducks are fairly shy and will leave the backyard if we go towards the pond. When the females starts to sit, she stays in the box, even if we mow the lawn right at the box, but if you open the door to her box, she will be off and not come back for several hours or more. We have two boxes, but a starling has scared them by sitting in the door to one of the boxes, so all three females that are laying are putting their eggs into one box. I think I have scared off the starling, but it will take awhile for them to try that box again. There was one egg in that box and I transferred it to the other box. Now we have twelve eggs in that box and none in the other box. We have put a camera in each box. So far the females have gone in and left before another enters the box but in past years we have seen some nasty fight when two females both get into the box at one time. Here is video taken in 2010--It was Fathers day. In this video you may see that one duck does not make it. He finally jumped after about 20 min. Mom was still waiting for him. Here is a link that might be useful: video 2010