Water Mill, United States offers 2 beaches perfect for sunbathing, surfing, swimming, and more. Water Mill is known for the Parrish Art Museum and its historic watermill. The best time to travel to Water Mill, United States, is during the summer months of June to August, when the average air temperature is around 75°F (24°C) and the water temperature is approximately 70°F (21°C). Sandee provides detailed maps, photos, and reviews from fellow beachgoers to help you Choose Your Beach™ and plan your perfect beach vacation!