Question
What must I do to the water before returning the gold fish to the pond?  

Answer
If this was a 100% water change, I suggest the following.  If you have city water, add dechlorinator.  Add some pond salt (half what the container says) and maybe some good bacteria.  Put back your plants if you have them as well as the non-living things including places to hide.  Start up the filter.  If it aerates well, then that's ok.  If not, add an air stone to heavily aerate the water.  If the pond is under 500 gallons, then heavy aeration for a few hours should be enough so the water is well oxygenated, and the temperature is stable.  When I clean out my 153 gallon pond (see http://www.fishpondinfo.com/myfish/clean.htm ), I do a 50% water change and heavily aerate for a few hours before putting back my minnows.  If your pond is more than 500 gallons, and the goldfish have a place to stay in the mean time, I would run and aerate the pond for a day before putting them back.  The main issues with the 100% water changes are chlorine/chloramine if you have city water, temperature (it should sit long enough to go to the ambient temperature as water from the tap is usually cold), and gases.  Water from the tap usually has compressed carbon dioxide in it and low oxygen levels.  I write about that at http://www.fishpondinfo.com/fishcare/water.htm#gas

Good luck!
Robyn