Flushing the Toilet and the Environment: Separating Fact From Fiction

Written by Leigh Matthews, BA Hons, H.Dip. NT


Leigh Matthews, BA Hons, H.Dip. NT

Sustainability Expert

Leigh Matthews is a sustainability expert and long time vegan. Her work on solar policy has been published in Canada's National Observer.


Ah, the great debate: letting the yellow mellow versus flushing every time. Yes, this is a gross topic, but also perhaps an important one as we all consider how to live a lifestyle that is easier on the planet. Water is a valuable resource that we must treat with respect, and toilets use water, so here we are.

Table of Contents
  1. “If it’s yellow, let it mellow”
  2. #1. Letting it mellow spreads germs
  3. #2. Not flushing saves nine gallons of water.
  4. #3. Not flushing saves a ton of money!
  5. #4. Pee is sterile
  6. #5. Letting pee sit makes it harder to clean your toilet
  7. In summary

Is there a hard and fast rule to follow for flushing your toilet in a way that is best for the planet? Does skipping a flush here and there really save you money and help ease the burden we put on Mother Nature? And just how wasteful is waste management? Here’s a look at how often you really need to flush the toilet, and why.

“If it’s yellow, let it mellow”

And “if it’s brown, flush it down.”

This little rhyme is well known to many of us, whether from childhood, camp, or media. But not everyone follows the mantra and some are staunchly against it. Reasons given for flushing every time include hygiene and respect, as well as making cleaning easier. The truth, though, is that it’s not always more hygienic to flush every time!

Let’s conquer some myths about the porcelain throne.

#1. Letting it mellow spreads germs

Leaving pee in the bowl instead of flushing it away seems gross and unsanitary to some. However, the science says that flushing every time actually spreads more germs. Yup.

Meet ‘toilet plume’ – the spray caused by that blast of water when flushing. This spray, which is a mix of fresh water and urine, leads to droplets floating about your bathroom and ending up on your clothing and skin.

Your best bet? Flush only when needed and always close the lid before flushing. Added bonus: closing the lid and letting it mellow also means less odor.

#2. Not flushing saves nine gallons of water.

Most people pee 6 or 7 times a day, so if you flushed every time and each flush used 9 gallons, that could mean using around 60 gallons of water every day just to flush. And if you have a nervous bladder, are pregnant, or have other reasons why you might pee more often, you could be using a lot of water every day if you flush each time.

Not so fast, though. Sure, not flushing saves water… but it’s very unlikely you’re using nine gallons each time you press that lever. Only very old, inefficient toilets use more than 7 gallons of water per flush. Most modern toilets only use about 1.5 gallons per flush, and even most older toilets use just 3-5 gallons. So, the water savings are actually fairly minimal.

In fact, in 1994, the US Environmental Protection Agency brought in a requirement for all toilets to use a maximum of 1.6 gallons of water for each flush. There are also an increasing number of WaterSense toilets that use 1.28 gallons per flush or less (while still matching or exceeding performance of toilets with higher flush volumes). WaterSense toilets have to meet rigorous standards and often come with rebates and vouchers to lower their cost.

Of course, not flushing does save some water. So, even if you have a highly water-efficient toilet that uses just 1.28 gallons per flush, that could still mean you’d save potentially 1400 gallons of water a year if you only flushed every other time you peed (3 fewer flushes a day, for 365 days).

There are other ways to save water though, albeit ones that feel rather removed. For instance, it takes around 660 gallons of water to produce an average ⅓ pound hamburger. So, even having a Meatless Monday every week would save some 34,320 gallons of water each year. And how about your jeans? Yup. Producing the average pair of denim jeans requires around 2,900 gallons of water, and that’s before you’ve even washed them!

So, yes, not flushing every time will save water, and every little bit helps, but don’t let that fool you into complacency in other more water-intensive areas of life.

#3. Not flushing saves a ton of money!

I hate to break it to you, but not flushing isn’t going to pay for your next vacation. At best, you might save enough on your water utility bill to cover the server’s tip on a poolside cocktail.

The average cost of a gallon of water is around 0.18 cents (that’s 0.18 cents, not dollars!) in the US. Assuming each flush uses 1.5 gallons and that you skip the flush three times a day, that amounts to around $2.95 saved each year.

Now, this will vary from state to state and even city to city. For instance, if you live in Florida, your savings will likely be much lower because water costs less. If you live in any of the following places though, you’ll likely save more by letting it mellow as these are the 10 states with the highest water rates:

  1. West Virginia
  2. Connecticut
  3. California
  4. New Jersey
  5. Utah
  6. Hawaii
  7. Washington
  8. Wyoming
  9. Kentucky
  10. Texas.

#4. Pee is sterile


Urine is quite surprisingly clean, but it’s not entirely sterile. Compared to saliva, urine contains relatively few microorganisms, with barely any while it’s in the bladder itself. However, urine picks up bacteria and other microbes as it passes through your system and into the bowl.

So, pee isn’t pristine, but it’s also not terribly germ-riddled. And there’s a good chance your municipal water has some residual germ-killing chlorine (unless you use a home water filter system). All of this means it’s fine to let it mellow for a few hours, ideally covered, before flushing the next time someone uses the facilities. If you have a urinary tract infection though, it’s a good idea to flush each time, especially if you share the bathroom with other people.

#5. Letting pee sit makes it harder to clean your toilet

This is the best reason I can find for flushing every time you pee. Why? Because the combination of urine and hard water (i.e., water that contains a lot of minerals), if left to sit for a few hours, can create a crusty deposit on the side of the bowl over time. Those stubborn rings might not seem all that bad, but if you end up using harsh chemical cleaners to get rid of them, the environmental impact becomes that much higher.

Thankfully, you have a few options here:

  • Install a water softening filtration system
  • Don’t let it mellow
  • Clean our toilet with milder cleaners at least twice a week, instead of once a week or less.

In summary

As we’ve seen, there’s no clear winner in the battle of the flush. Whether you’re feeling mellow or militant about flushing, there’s something to be said for both sides of the argument. Either way, if you don’t have a modern toilet with a high-efficiency flush, it’s time to upgrade or take other steps to curb water usage. This could be as simple as putting a plastic bottle filled with water and a few rocks or pebbles into your cistern, so less water is used per flush.

You might also consider peeing in the shower… though this is one to run by your family and/or housemates first if you don’t live alone.

And if you do decide to upgrade, consider a WaterSense certified toilet, so you can be sure you’re saving water without losing out on performance.

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  1. Another aspect is wear and tear on the flush mechanism. With a simple old style lever and chain, not too much of a problem. The flush on my lavatory, however is push-button and enclosed, and could be expensive to repair. The basic rhyme is sound enough as so much water is wasted flushing piss. Wait for a turd or two is my motto as well.

    Perhaps it would help if cisterns were either filled with rainwater, seawater or water which was not suitable for drinking or washing. One statistic about very little of the world’s water being useable should mean different sources should be used for flushing the bog…

  2. Where on earth do you get 7 gallons from? That is huge! According to Which? the average pre 1995 cistern used less than 10 litres per flush. 7 US gallons is over 26 litres.

  3. Okay so my problem is with the math?:

    “The average cost of a gallon of water is around 0.18 cents in the US. Assuming each flush uses 1.5 gallons and that you skip the flush three times a day, that amounts to around $2.95 saved each year.”

    0.18 cents a gallon x “1.5 gallons” each flush (let’s just assume we only flush ONCE a day) x 365 days a year = $98.55 a year! NOT $2.95!?!?!?!?

    Soooooo… please explain your mathematics here???

    • Hi Evee,
      Thanks for the comment. I think there’s been a misunderstanding here as to what 0.18 cents means. This doesn’t mean 18 cents (which would work out to savings of $295 per year).

      To clarify my math a little further:

      1 gallon of water = 0.18 cents (or 0.0018 dollars)
      1 flush = 1.5 gallons = 0.27 cents (0.0027 dollars)
      3 flushes fewer per day = 4.5 gallons saved = 1.215 cents (0.01215 dollars) saved
      365 days = 1095 flushes = 1642.5 gallons saved = 295.65 cents (2.9565 dollars) saved

      I added the emphasis of cents not dollars in the article in the hope it helps make things a little clearer for other readers too.

      Hope that helps,


  4. Conflicting information- in the beginning of this article “… that could still mean you’d save potentially 1400 gallons of water a year if you only flushed every other time you peed…”

    Near the end of the article it is suggested that you flush about every two hours for I believe you said hygiene purposes. I don’t need to pee in two hours. So every other time as stated in the beginning could be anywhere from 3-4 hours for me.

  5. Regarding #1 Letting it mellow spreads germs. The statement about a plume of water/urine upon flushing should never happen in a home toilet. That sounds more like a commercial pressure type flush that would cause any “plume” (you know when the rest area toilet flush sprays your bum). Closing the lid when flushing is common sense, UNLESS you have had any close calls recently with overflowing. Sometimes the very next flush is the one that ends up on the floor, and by having the lid open, you might see it coming and grab a plunger just in time to avoid that mess.
    However, always flush after peeing. Always. Urine left habitually over night + hard water = layers and layers of very difficult to remove scale at the bottom of the bowl. Why would anyone want to deal with that? And guys, if you have a home with a yard and trees go out there at night to pee around the trees. Move to a different spot each time and you will 1. Not contribute to toilet buildup 2. Not use a drop of water each time 3. Fertilize your trees! I’m that guy lol!

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