I remember hearing this expression when I was very little. I guess I understood the basic concept but I didn’t really understand why. My grandmother lived in a cottage that relied on well-water and I was told it uses less water.
One of the largest consumption of water (after the shower) is the toilet. Especially if we consider that we use the toilet multiple times per day and the shower only once per day (or every two days if you can manage that).
Toilet Water Consumption
Old toilets can use up to 6 gallons (20L) of water per flush! Thankfully, there aren’t that many old toilets left. Most modern toilets use 1.6 gallons (6L) of water per flush and some super efficient ones can use as little as 1.28 gallons (4.8L).
Toilet versus Shower/Bath
When we compare water consumption of toilets and showers/baths, we see that an individual flush is not much water. However, if we consider the FREQUENCY at which we use the toilet compared to the shower, the clear water guzzler is the old toilet and even water efficient toilets use almost as much water as showers yearly.
How much water can you save?
The expression “If it’s yellow, let it mellow. If it’s brown, flush it down” was apparently first used during one of the earlier Californian droughts. It basically means what it says: flush only after defecation, not after urination. Urine in the toilet doesn’t necessarily have a bad smell (at least compared to feces). Furthermore, it’s been proven that flushing the toilet releases fine particles in the air that dirties surfaces and toothbrushes, so the less often we flush, the less these particles enter the air. If you flush only twice per day (let’s say someone stools twice per day, though this ranges a lot), you can save as much as 66% of water!
So think about it next time you use the toilet.
References
(1) https://www.epa.gov/watersense/residential-toilets#:~:text=Specification%20Revision-,Flush%20Facts,of%201.6%20gallons%20per%20flush.
(2) https://www.google.com/url?sa=t&rct=j&q=&esrc=s&source=web&cd=&ved=2ahUKEwjUrq61q7KCAxX7GzQIHX9ZAyIQFnoECAgQAw&url=https%3A%2F%2Fthelumberjack.org%2F2019%2F04%2F12%2Flet-that-yellow-mellow%2F%23%3A~%3Atext%3DMany%2520homes%2520across%2520the%2520country%2Con%2520how%2520old%2520it%2520is.&usg=AOvVaw0i27bM_W3V216m9lCCyN4B&opi=89978449
(3) https://www.yourdictionary.com/if-it-s-yellow-let-it-mellow-if-it-s-brown-flush-it-down#:~:text=Origin%20of%20If%20It’s%20Yellow,one%20of%20the%20California%20droughts.