eli5 Is there a reason the waste water like from showers can’t be filtered through pipes and used for toilet water?
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It is best for the cleanliness of the inside of your toilets to keep fresh, clean water in and dirty water out.
Also waste water is treated at water treatment plants and then recirculated. It is very hard for water to be cleaned so large plants are needed. It must be centralised because of this.
Shower water (grey water) and sewage (brown water) generally should not be mixed together. Science knows a lot, but we don’t yet fully understand how the chemicals you shower with interact with the chemicals that come out of you.
Remember, you’re not just mixing food and water: we’re taking supplements, pesticides, hormones, drugs, and medicine. Mixing that with the list of chemicals found in your shampoo can have ugly effects in the filtration process.
“Grey water” is sometimes reused in places where clean water has to be trucked in, but not typically for places where you’d see or smell it.
If your dishwater ended up in your toilet that would be pretty nasty.
Non-sewage household water (from, e.g., showers, sinks, dishwashers, etc.) is called graywater and in certain circumstances is captured for particular uses, largely watering lawns or gardens (especially at night). It’s still fraught with potential dangers since graywater can carry pathogens from people washing their hands, etc., so it’s seldom used except in places with serious fresh water limitations. And even then, graywater systems are designed to prevent people coming into contact with graywater.
Circulating such water through toilets introduces risky potential contact points for people and pets. Flushing a toilet spreads a fair amount of water droplets (and other things) through the immediate area, so it’s best to avoid untreated water. Also, there’s lots of engineering and expense needed to create a separate water circulation system – you’d need to address water pressure issues and essentially pump used water into a storage tank connected to toilets with adequate backflow preventers, and ensure that there’s always enough water to flush with (or create an entire secondary supply system). And for all that, you’re capturing maybe 20-30 gallons of water per shower. That’s enough to flush a toilet 20+ times, but that seems an unsustainable ratio – do you flush a toilet 20 times for each shower you take? So you’re going to have to dump water out of the system anyway unless you have enormous tanks or some way of connecting your system to some large venues that use toilets but not showers (like sports stadiums).
In short, it can be done, but the design and engineering difficulties are enormous and the benefit is minimal.
It certainly *can* be, but in most places it’s not done simply because it would add more complex plumbing and filtration systems, which adds costs and more possible points of breakage/failure.
Graywater systems are used in some places, but they generally take water from washing machines and showers and use it for landscaping. It’s not usually seen as worth the hassle to capture gray water for indoors use.
There are also risks, like getting dirt someone washed off their hand splashed on sensitive areas while using the toilet, or even just having the residue from ammonia dish detergent mix with bleach used to clean a toilet.
So you’re on the right track with your idea, but the reality is that there are complications and costs that make only the simplest forms of graywater reuse practical.
I can recall being in the keys in Florida, and the hotels and resorts use treated grey water for the toilets.
it can be, it is called grey water, but it means doubling up the number of pipes and making absolutely sure you don’t mix the two. So it rarely makes sense
A Japanese toilet that recycles hand-wash water for the next flush.
https://static.tnn.in/photo/msid-94836575,imgsize-13990,updatedat-1665661413207,width-200,height-200,resizemode-75/94836575.jpg
Also cheaper to install as only one water supply is needed.
Murfreesboro TN offers the effluent from their sewage plant to developers for irrigation and toilet flush water.
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