100 years ago, the first international plumbing congress was held in Paris. This was a first effort to standardize plumbing regulations and product manufacturing. Standardization around the 2 inch (50 mm) water seal for traps was one outcome, which effectively established a uniform pressure limit.
John Lansing
The harmonization effort was led by an assembly of national trade unions, recognizing the need to provide rational guidelines for designing and installing plumbing systems (and roofing interestingly) with some level of uniformity.
