Changing Duck Water (me again..)

Look at your other posting for my other response that overlaps with this. We change pond water every 2 months perhaps every month in summer. We have a submersible pump but that leaves an inch or so to be swept into a pail and thrown out. We have ducks at home so water and power easy to get at. They also have cut down barrel we change every three to four days when we change bedding -- it is meant for drinking and face dippinng  but they still get in it sometimes. They also have fresh water every day when we feed just for drinking which is in a smaller bucket they cant get bodies into and it has a brick in the bottom to stop them knocking it over (learnt the hard way)
R