Ducks and geese love to swim, and they are EXTREMELY cute when they frolic and play in water (don't believe us?...then watch the "Ducklings enjoying bath time!" video in this article), but you are making some headaches for yourself if you provide them with continual access to swimming water. The biggest problem is what to do with the water after they have muddied and defecated in it so it becomes dirty. It is not safe or healthy for them to swim in a putrid pond, so the water will need to be changed regularly.
If you do provide swimming water, they certainly don't have to have it every day. You can limit it to a few times a week, using a small kiddie pool, masonry mortar pan, or shallow feeding trough--something easy to turn over or drain and move to a different location as needed to avoid accumulation of mud. Ideally, you can use the dirty water in the garden. The plants will love it!
Duckling enjoying her personal "jacuzzi."
Be aware that waterfowl can drown in deep, steep-sided pools. Make sure that the pool or small pond you provide has low-slope ramps with good traction on the sides so the birds can get out and avoid becoming trapped inside the water.
Because their fluffy feathers can become waterlogged leading to chilling or drowning, birds younger than two weeks of age should not be given access to swimming water.
One more thing to consider: some larger breeds of ducks and geese mate much more easily on water, so if you want to have fertile eggs for hatching, some breeds of ducks and geese will need fairly consistent access to swimming water during the mating season. Watching ducks and geese swim can provide hours of entertainment--and hours of clean-up!--but everyone can enjoy "pool time" if you plan for and manage it carefully.