The curse of the auto flush toilet

Last week, Brian and I took our first honest-to-goodness overnight trip in over a year. The vaccines arrived too late to allow us to make our usual trip to Indiana for Christmas last year, so to make up for it, he took a week off and we drove out to visit his folks for a few days. It's a twelve-hour trip by car, so we naturally have to make several stops along the way — usually just one for a meal, but quite a few to use restrooms. And so I had my first reminder in over a year of one of the biggest problems with public restrooms: the capriciousness of auto flush toilets.

I'm not the only one who finds these thing annoying. Search "why are auto flush toilets so bad," and you'll find multiple threads on Reddit complaining about them (usually in very bad language, so you've been warned). The problem is, to know when to flush, they rely on an infrared sensor that is, in theory, blocked when someone is seated. So every time the light hits that sensor, it assumes that someone has just gotten up and flushes. But in reality, it's almost impossible to enter a stall, sit down, do your business, get up, and exit without uncovering the sensor multiple times, resulting in multiple flushes. In some restrooms I've visited, the toilet regularly flushes at least once before I even sit down.

Now, there are several reasons to be annoyed by this. Maybe you don't like loud, unexpected noises, particularly when you're in a public place and partially disrobed. Maybe you don't like having your bum sprayed with water. Maybe you're a parent whose small child gets freaked out (not unreasonably) at having the potty suddenly threaten to suck them in while they're sitting on it. But for me, the most frustrating thing about these "phantom flushes" is that each one of them wastes water — according to the EPA, at least 1.6 gallons (the current federal standard) and, in the case of some older models, more than four times that amount.

How much waste does this add up to in total? There don't seem to be any recent studies on this point, but according to Grist, a 2010 study (no longer available online) found that water use in one office building increased by 54 percent after it installed auto flush toilets. Multiply that by all the 27 million toilets in the U.S. that use these infernal inventions, and you're talking about a lot of wasted water. Think about what you could do with all that extra water in a place like California, which lives in a perpetual state of drought. According to a 2015 Los Angeles Times op-ed, eliminating auto flush toilets just in the state's two biggest airports, LAX and SFO, could save 80 million gallons per year. Replacing all the auto flush toilets in the state with manual ones would save billions of gallons.

And yet the EPA, which has a mandate to prevent water waste, does not propose this solution. Instead, it suggests that these 27 million toilets should all be replaced with WaterSense models, which use less water per flush. And admittedly, wasting 1 gallon of water on each phantom flush is better than wasting 1.6 gallons. But it would do nothing at all to eliminate the phantom flushing problem. A manual flush toilet that uses 1.6 gallons of water for one flush per use is still a lot more efficient than a so-called WaterSense toilet that uses 1 gallon each for three or four.

A real solution would be to make better sensors that don't go off until the user is actually done with the toilet. My first thought on this point was that maybe instead of an infrared sensor, the toilet should have a sensor under the seat that detects a person's weight, so it would only flush after the person has actually finished and stood up. But I quickly realized there were two problems with this. First, apparently some people prefer to stand up to wipe, which means they might not be done before the flush occurred. But more seriously, apparently many people never sit down in public restrooms at all. Again, I couldn't find a recent study, but a 1991 study in Britain found that fully 85 percent of women — 85 percent! — prefer to "crouch" over the seat to avoid contact. (Another 12 percent routinely covered the seat with paper, leaving only 2 percent who dared to allow their bare butts to make contact with the seat.)

So here's my new idea: don't put the sensor on the toilet at all. If you want to have an automatic flush toilet, have it be triggered by the opening, or perhaps the unlocking, of the stall door. That would absolutely guarantee that the toilet won't flush until the person is done using it. You might still get a few phantom flushes from people who only went into a stall to change clothes or something, but it would be far less than the number we're getting now.

Unfortunately, I don't have the engineering know-how to make this work, nor the connections to get such an invention distributed. But anyone who does is more than welcome to steal the idea. I'm happy to forfeit any financial gains from it in exchange for the benefits of less wasted water all over the country, and less annoyance to me and millions of others every time we use a public restroom.

In the meantime, I guess I'll have to make do with the low-tech solution outlined in the Grist article: covering up the sensor with toilet paper or a Post-It as soon as I enter the stall, and removing it when I leave. So, essentially, turning the auto flush toilet into an overly complicated version of a manual flush toilet. This won't always work, because as I noted above, there are some toilets with sensors so oversensitive that they flush reflexively pretty much the second you walk into the stall. But at least it will reduce the flush rate to two per visit — only twice as many as necessary — instead of three or four.