Simply put a bowl inside to actually hold water and add the colander just for looks. We like how a colander lets the round little arrangement perch up on feet on the tabletop.
Of course, you could use an old, rusty, non-kitchen-suitable colander for this too. A great reuse of an object that might otherwise be thought past its useful life! See more images of the example above at Family Chic.
(Image: Family Chic)