Mallards prefer to nest in areas with tall grasses, reeds, or other vegetation near water. This provides cover and protection for the nest and the ducklings. Without water nearby, the mallard may have difficulty finding food and water for itself and its young. Additionally, the ducklings may not be able to learn how to swim and forage properly if they do not have access to water.
If you find a mallard nest outside of your house, it is best to leave it undisturbed and allow the ducks to raise their young. If you are concerned about the mallards' welfare, you can provide a shallow dish of water nearby to help them stay hydrated. You can also try to discourage them from nesting in that location by removing any vegetation or nesting materials that they may be using.