Eli5: Why do we use clean, potable water in toilets?
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The question we should be asking is does it make sense to treat 100% of our water to potable standards when 99+% isn’t used for drinking? We can cheaply produce crystal clear disinfected water for household use but it’s getting real expensive to remove parts-per-billion of chemicals from all the water just because someone may drink a glass of it. It’s terribly inefficient. Someday society might just decide that it’s not worth it if you can buy your drinking water or use a home filter for drinking.
Try not flushing it and using your urine to clean the bowl.
It will save my typing and confer what text alone can not, that is to say the smell.
My parents have a dedicated grey water system for toilets, dishwasher and washing machine in their house. It runs on groundwater which gets drawn from 20m below their home.
I know some other people who have similar systems installed over here in germany.
There is a trade-off between the amount of plumbing complexity and the amount of water saved and reused. In most countries, we use what is basically the simplest system: one tier of water, used from everything from toilets, to irrigation, to drinking. This means everyone needs one set of water delivery pipes, the streets need only one set of water delivery pipes, etc. The downside is that a lot of water (about 680L per person per day) needs to be processed up to drinking standard, while only about 2 litres of that is drunk. In my city, they charge NZD$237 per year for water, and even in Las Vegas, it’s only NZD$2.37 per 1000L .
In some buildings, “grey water” from sinks, showers, and baths is recycled for use in toilets and irrigation. It can also be treated and recycled for sinks and showers. This can decrease water consumption by 30%, and water heating by even more. At current prices, it is often cheaper just to use potable water and not bother with a grey water system. Even when it is cheaper in the long run to install a grey water system, the developers don’t see the benefit because it will be someone else paying the water bill.
However especially in desert areas, a far cheaper and more effective water-saving measure would be to stop watering your garden and replace anything that dies with native plants specifically evolved for your neighbourhood conditions.
I can talk more about the plumbing complexity involved in a municipal grey water system, let me know if you’re interested.
I use a big bucket when I get a shower and then use it to water my plants and flush my toilet, I haven’t used potable water to flush in a while.
It’s pretty standard in Australia to not use potable water in the toilet, at least not as the default option. Building regulations for at least a couple of decades now have required all new houses to direct rainwater from the roof into storage tanks. That gets used in things like toilets and on gardens. If the tanks run out there’s a valve that flips to direct potable water into the lines instead.
We don’t have to. Historically it’s been cheaper and more conveniënt, but with water becoming a more valuable resource many places around the world are using treated waste water or just locally stored rainwater.
Engineering explained has got an excellent video on the matter: [https://youtu.be/sUoO_U_GWFo?t=594](https://youtu.be/sUoO_U_GWFo?t=594)
Here in Belgium new constructions REQUIRE a rain collection system that is used for toilets and laundry. When doing renovations, the state subsidizes these systems in an effort to mitigate climate change and lowering levels of ground water. I believe it’s similar in other EU-countries.
Many have answered: just was simpler, cheaper and less headache for plumbers and city systems.
There is some movement to have toilets and urinals using storm water from the roof of large buildings. This is isn’t super difficult to engineer, since a lot of big buildings have mechanical rooms on their top floors and you can have storage tanks up there.
The other answers are all generally correct, but it is worth mentioning that there are some places where there is a separate non-potable water system that uses treated wastewater for things like toilets, irrigation, etc. So it’s not so much that it is a bad idea, just an expensive one — particularly in places where the infrastructure isn’t being newly laid down.
Home water systems work like a tree. The big line is the trunk and it branches out to things like your shower,toilet sink etc. And the reason we use clean water is for sanitary reasons.
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