Water pipes in hydroelectric power station. Free public domain CC0 image. https://www.rawpixel.com/image/6030208/photo-image-public-domain-nature-freeFree Image from public domain licenseBill Walker and wife Emma in surge chamber no 1, Mangahao Hydro-electric power station (20 May 1923) by Leslie Adkin. https://www.rawpixel.com/image/13028855/image-person-technology-circleFree Image from public domain license