Waterless urinals were first invented back in 1991. But the invention has only started to be adopted more widely since around 2006. That year, urinals were accepted as an alternative specification in both the Uniform Plumbing Code and the International Plumbing Code [source: Davis]. Those two codes serve as the basis for most state and municipal plumbing codes in the United States. After this landmark, waterless urinals were made legal in most parts of the country. Before that, only a small number of local governments had enacted their own laws making waterless urinals legal. The plumbing profession argued that waterless urinals were unsafe, prone to allowing toxic sewer gas to escape from drainage pipes. Once the plumbing industry was convinced that waterless urinals could be installed safely, thanks largely to improvements to the technology, states began to rewrite their plumbing codes to allow them [source: Davis].