Yes, indoor plumbing was used during World War II. Indoor plumbing had already become commonplace in developed countries by the time World War II started in 1939, with the notable exception of rural areas. In urban areas, most homes and buildings were equipped with indoor plumbing fixtures such as sinks, toilets, and showers, connected to a network of pipes and drains. This allowed for the convenient provision of clean water and removal of wastewater, improving hygiene and sanitation significantly. Even some military camps and field hospitals during World War II were equipped with portable or temporary indoor plumbing systems to maintain proper hygiene and living conditions for soldiers.