Eli5: Why are most public toilets plumbed directly to the water supply but home toilets have the tank?
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In order for a toilet to flush, you need a high volume of water in a short period of time. The tank stores this volume and the toilet is designed to deliver it all at once. Basically, all that water builds up momentum which flushes everything along with it. Residential plumbing is not designed to provide that much volume in a short period of time, but commercial plumbing usually is.
Imagine the overall water pressure if everyone flushed at once?
In order for a toilet to flush, you need a high volume of water in a short period of time. The tank stores this volume and the toilet is designed to deliver it all at once. Basically, all that water builds up momentum which flushes everything along with it. Residential plumbing is not designed to provide that much volume in a short period of time, but commercial plumbing usually is.
Imagine the overall water pressure if everyone flushed at once?
If you look at a commercial/public toilet in the US, you’ll notice that it’s fed by a 1-1/4″ or 1-1/2″ water supply pipe. That’s so it can supply enough water volume to forcefully flush. Most residential homes are fed by a main pipe that is only 3/4″ in diameter, and cannot supply enough volume to flush a commercial toilet. So, to work around that, residential toilets have a tank to store some amount of water, which on flush, drops into the toilet bowl with sufficient volume to flush the toilet, then the tank slowly refills for the next flush.
Imagine the overall water pressure if everyone flushed at once?
If you look at a commercial/public toilet in the US, you’ll notice that it’s fed by a 1-1/4″ or 1-1/2″ water supply pipe. That’s so it can supply enough water volume to forcefully flush. Most residential homes are fed by a main pipe that is only 3/4″ in diameter, and cannot supply enough volume to flush a commercial toilet. So, to work around that, residential toilets have a tank to store some amount of water, which on flush, drops into the toilet bowl with sufficient volume to flush the toilet, then the tank slowly refills for the next flush.
If you look at a commercial/public toilet in the US, you’ll notice that it’s fed by a 1-1/4″ or 1-1/2″ water supply pipe. That’s so it can supply enough water volume to forcefully flush. Most residential homes are fed by a main pipe that is only 3/4″ in diameter, and cannot supply enough volume to flush a commercial toilet. So, to work around that, residential toilets have a tank to store some amount of water, which on flush, drops into the toilet bowl with sufficient volume to flush the toilet, then the tank slowly refills for the next flush.
Having no tank means you have to rely on a high water pressure for it to flush properly. Not many homes have the required mains pressure, and high mains pressure is bad for your appliances, taps, washing machines, water heaters, etc anyway, so using a tank makes up for the lower pressure. It’s also much quieter so flushing the toilet won’t wake up your neighbors (a tankless toilet makes a horrible flushing sound).
And for public toilets, simplicity and maintenance is a priority, and tanks are more prone to breaking, leaking or being tampered with. And with no sensitive appliances, high mains pressure is not an issue.
In Germany more toilets are directly on the mains supply, especially in buildings from the 50s to 70s. But the water tank toilets can save water, as the direct flush toilets push out too much water very fast. Nowadays modern public toilets also use the tank system and have a split button on them, the smaller for pee and the larger for solids.
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