Imagine if all the 350 million toilets in the US were flushed at the same time. This will require efficient coordination, but the question is what would happen if this is pulled off successfully. This is a complicated experiment and experts are not sure how things will go down. However, it is likely that a total system failure will not occur. According to a civil engineer at the Utah Water Research Laboratory, Michael Johnson, who models the fluid flow in the sewer systems, The consequences of mass flushing will range from negligible to pipe explosions depending on where you are. He said, “Because each city has its water supply system, the effects of the flush would be localized.”
In some areas, the biggest issue will be the shortage of water for refilling at the local commodes at once. Since there is a very low probability of getting a universal bathroom break, therefore, not all water towers and tanks store 1.6 gallons for every toilet where they are supplying. In such places, constant flushes will leave some toilets dry and wait to get a refill. This can result in a severe plumbing problem when the air is introduced into the supply line. Johnson said, “Air in a pressurized water system is very dangerous as it can move very quickly through the supply lines and consequently result in serious water hammer.”
Water hammers are pressure surges which are caused by a sudden drop in the velocity of water through a pipeline. This can cause the rigid pipelines to explode. Cleaning and emptying a pipe even for a second introduces compressed air inside it, and when the water flows into the tube and encounters the air pocket, the water comes to a halt. The pressure built inside the pipe can cause a pipe explosion. Many other cities can handle this without the risk of a water hammer. Ed Maurer, a civil engineer at Santa Clara University and hydraulics, said, “I would think that most cities have water supply systems that are robust enough to handle the refilling of all toilets simultaneously. For example, if one tank served 25 percent of my city (25,000 people) and even if we assume everyone had their toilet to flush, the standard 1.6 gals/flush toilet will create a total need for 40,000 gallons, which is equivalent to a small pool.”
The outgoing sewage might be saved from the plumbing disaster due to simultaneous flushes which don’t seem simultaneous if seen from the main sewer line. Johnson said, “A simultaneous flush would result in sewage arriving at the main trunk line from toilets further from the branch connection arriving much later than sewage nearer the branch to trunk connection.” In other words, the main line would receive a smooth curve of commode contributions. However, there are chances that the plumbing in some apartment buildings get backed up when all the residents flush at the same time depending on the layout of the building’s pipeline. There are also chances that two underground branches meet simultaneously at the main line and cause a backup.
In some old East Coast cities, the storm and sanitary sewers converge during heavy rainstorms and cause sewage to get dumped into rivers and bays with the overflow. Maurer said, “If there are bottlenecks in the system, perhaps they could be overwhelmed, but I would not expect worse than we already see periodically. If there are bottlenecks in the system, perhaps they could be overwhelmed, but I would not expect worse than we already see periodically. That regularly causes public health issues already. Would a massive simultaneous flush produce more flow than an intense rainstorm? No.”
Apart from minor mishaps, no expert predicts a significant system collapse from collaborative flushing. The American Society of Civil Engineers regularly grades the United States infrastructure and as a nation, they are classified as D. Maurer said, “Our sewers, water systems, and other crucial infrastructure is severely underfunded. So maybe there will come a time when a massive toilet flush will have a bigger impact!”