Before construction reforms were introduced in the early 19th century, liquid waste would seep away through the ground, leaving solid waste behind in the cesspit. While this made removal of solid waste easier, the seeping liquid waste often contaminated well water sources, creating public health problems. Municipal reforms required that cesspits be built of solid walls of stone and concrete. This kept liquid waste in the cesspit, forcing cesspits to be cleaned more frequently, on average two or three times per year. Liquid cesspit waste would be removed with pumps by cesspit cleaners, and then solid waste, valuable as fertilizer and for manufacturing ammonia, was removed.