Pond water is fine. In fact, it tends to be rather nutrient rich compared to tap water.

No worries. I used to use the water from my aquarium water changes, and my plants loved it. Critters that live in the pond excrete urates that are broken down by beneficial bacteria into nitrite, and eventually broken down further into nitrate. Both are forms of nitrogen, which is the "N" in the NPK rating of fertilizer.

Same here. My pond is on a slope, and I often siphon water out with a hose for plants on the downhill side. They seem to thrive.

In many if not most cases, the primary factor that determines where nursery and greenhouse ops are sited is the quality of the water available. Critical parameters re anion and cation content, as well as pH are evaluated before a property is purchased. This is especially true when surface water is the source of water to be used for irrigation. The same guidelines that determine whether or not a water source is suitable for greenhouse or nursery production, would also be the yardstick by which it would be determined whether or not the water is suitable for use by the hobby grower.

So, without knowing if the pond water is within critical parameters, it really can't be said whether or not it is appropriate for long term use on plants by the hobbyist. I'm thinking the best we can say is, "You'll have to try it and see, or send it in to a lab for testing if you want to make an informed decision". Too, it's more critical if you're using the water in question on containerized plants.

Al