Jeff and I visited some friends in Salt Lake City a few years ago, and our host forewarned us that she only flushed the toilet for number two’s, so please excuse any pee that you might find upon entering the loo. Okaaaay. Seemed kinda weird, but she mentioned it was more of a water conservation thing than weirdness. I realized it totally made sense.

Let’s drop some knowledge on toilets. Before 1994, most residential and commercial toilets used about 3.4 gallons of water per flush. Due to congressional policies, beginning in 1994 toilets began using only 1.6 gallons of water, and now high efficiency toilets use 1.3 gallons of water.
Did you know that 26.7% of your daily residential water use is from using the toilet? That’s 26.7% of 350 gallons, the average daily household water use. Let’s carry out the math…that’s 93.45 gallons of water a day, on flushing your toilet. Think of how many times you flush the toilet just for number onesies. That’s a shit-ton of water! (Disclaimer: I don’t think “shit-ton” is an actual measurement of any kind. It’d be awesome if it was though).
Total prolonged sidebar: I was amazed when I was in Haiti how little water you really need to shower. I would fill up a 5 gallon bucket of water about 3/4 of the way for bad days, and maybe a little less for days I didn’t feel as gross. It’s totally enough. Think about how many 5 gallon buckets of water you could fill with the amount of water you use to shower. I tried visualizing it the other day and just gave up. One easy way to cut back is to use the Guatemalan water conservation method. In Guate, you don’t have running water all day, so you store up your water in the morning, and use those water deposits throughout the rest of the day. When showering, most people turn off the water when they’re soaping up so they don’t waste that water, then turn it back on to rinse off. I’ll confess that I don’t do this: I like having hot water running the whole time…why would I turn it off and freeze while I soap up?! BUT, I should. And I will try to be better about it.
Back to pee.
In searching online, I agree with most people that flushing after a one or two is appropriate when you’re at other people’s homes (duh), if you have guests, and if you have small children or pets around that are likely to go digging in toilet water.
Aside from those specific concerns, I’d only be worried if it was unsanitary.
On the EPA website with tips for “How to Conserve Water and Use it Effectively,” it states: “Toilets should be used only to carry away sanitary waste.” The attorney in me would like a definition for “sanitary waste.” Does it include urine? According to the Utah Water Quality website, “sanitary waste” is “liquid or solid wastes originating solely from humans and human activities…” Damn.
I searched various phrases relating to “urine” and “sanitation,” but most of them involved drinking pee. That’s definitely not my concern. One comment mentioned that urine takes 24 hours outside the body before it starts to grow anything. I don’t think I go more than 24 hours without flushing our toilet. One comment I thought was pretty funny was someone concerned about the level of ammonia produced by urine, and how letting it sit in your bathroom will make it more difficult to breath (due to the increased levels of ammonia, duh). Maybe s/he has a really small, enclosed bathroom?
My take on this research: it’s ok to not flush for onesies, just make sure you flush every now and then.