Keep the water depth shallow, no more than about five centimeters at the deepest point, since most backyard birds cannot use a bath that is too deep and a shallow basin with a gently sloping edge lets birds of different sizes wade in safely. Choose a rough-textured basin rather than a smooth, glossy one, since smooth surfaces become slippery when wet and give birds nothing to grip with their feet, making them hesitant to land or bathe. Place the bath in a spot with some nearby cover, like a shrub or low branches a couple of meters away, since birds need a quick escape route from predators but also need enough open space around the bath itself to spot danger coming. Change the water every two to three days even if it looks clean, since standing water left longer than that becomes a breeding ground for mosquito larvae regardless of how clear it appears. Scrub the basin with a stiff brush every week, since algae and bird droppings build up a slick film that is easy to miss visually but still poses a health risk to the birds using it. Add a few flat stones or pebbles to the bottom of a deeper basin, since these give smaller birds a shallower perch to stand on within a bath that might otherwise be too deep for them.