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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A similar idea is to use non-potable water (eg untreated well water) for all things in the house (showers, toilets, lawn, washing,etc) but have a potable water system only for drinking water (fresh drinking water tap at the sink, ice maker, pot filler, etc).
One thing that you can do is recover the heat from the water in the shower with a device called a GFX (Greywater Film Exchanger)
See: https://gfxtechnology.com/index.html
The city of Hong Kong does a lot of grey water use. There are a lot of people there and anything that can be done to reduce drinking water usage is very important.
Grey water can be used to reuse water in a building multiple times before it exits the building through toilets and other drain points.
The most uses out the water can be:
Drinking water or other clean water use (showers, sinks, laundry)
Sterilize with UV/ozone treatment
Drain to Planter and water plants.
Drain the excess to toilet usage – and then out of the building. Depending on where you are this goes to city water reclamation or a septic tank. and the run off from the septic tank can be used to water gardens, lawns, etc.
You can also introduce rain catches into this and introduce that water at the planter tier.
I am skimming over a lot of discussion about the technical requirements, piping and implementation.
In practical terms, greywater still has enough oils and soap residue that the toilet tank and bowl would get grimy pretty quickly.
In some jurisdictions that permit separate greywater plumbing systems, it can be sent out of the house to a settling or treatment tank and then used for things like plant irrigation.
Also, if it’s going to be distributed in pipes indoors, the pipes need to be clearly marked “not potable” so someone in later years doesn’t assume it’s clean water and hook it up to a sink. The same is true for rainwater: if it’s collected it’s difficult to get permission to use it for things like toilet flushing. (I negotiated with the State of Illinois for two years to come up with a system design that would be allowed by the health department.)
In Japan, I encountered two interesting things related to greywater reuse. One was toilets that had a hand-washing sink just above the toilet bowl, so the water from that would be used to flush. The other is that once the whole family has used the soaking bathtub (ofurō) they would use a siphon from the washing machine and transfer the hot water from the tub to do laundry with.
Certain LEED certified level buildings do this. There’s no reason you can’t, it just costs more money and requires storage tanks to hold the grey water used to flush the toilets and the like.
It would be simple enough with new construction, but for older houses it would require a complete replumbing of the entire house.
Furthermore, most bathrooms contain the shower and the toilet and the toilet is always higher than the drain of the shower. So you need some way to pressurize that drain water to lift it high enough to be used in the toilet, which requires pumps or other devices.
You can actually get a replacement lid for your toilet that turns it into a sink.
You do your thing in the bowl. Lower the lid. Flush. Then as the tank refills you wash your hands with the clean water filling the tank.
[like this](https://www.amazon.ca/SinkPositive-GreenFlow-Toilet-Tank-Faucet/dp/B0BYLKF4T5/ref=sr_1_6?crid=3MLWN7H2FQWJF&keywords=toilet+sink+lid&qid=1695605454&sprefix=toilet+sink+lid%2Caps%2C230&sr=8-6&ufe=app_do%3Aamzn1.fos.b06bdbbe-20fd-4ebc-88cf-fa04f1ca0da8https://www.amazon.ca/SinkPositive-GreenFlow-Toilet-Tank-Faucet/dp/B0BYLKF4T5/ref=sr_1_6?crid=3MLWN7H2FQWJF&keywords=toilet+sink+lid&qid=1695605454&sprefix=toilet+sink+lid%2Caps%2C230&sr=8-6&ufe=app_do%3Aamzn1.fos.b06bdbbe-20fd-4ebc-88cf-fa04f1ca0da8)
Water needs to be under pressure to go uphill, like from the toilet shut-off valve up into the tank. But when water from the main supply leaves a faucet and enters a drain, it loses all pressure.
So a water-capture system would need some way to repressurize the water in order for it to be useful. There’s ways to do that, but they’re largely mechanical, and any time you have mechanisms in contact with water, the useful life of those mechanisms is hugely degraded by the presence of just about anything *in* the water.
It’s just easier to plumb a toilet from mains water because it comes pressurized from the main – it already contains the useful energy you need for it to be forced up into the toilet tank. Mains water is cheap enough that it doesn’t make a lot of sense not to “waste” it in toilets (it’s actually not a waste; toilets are the most important use of water in the household, probably.)
We have our shower and washer water just run out the side of the house as grey water vs the septic tank. Not reuseing technically though. Worried prob stink after a while if not flushed right away
Youi can install a catch-basin, and then pump it up to an elevated cistern that feeds the toilets.
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