Eli5: Why do we use clean, potable water in toilets?
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Using grey water to flush toilets would require storing said grey water and pumping it through the toilet.
Simply put; using fresh water is easier since the toilet can be hooked up to already existing water sources/pipes.
What are the other practical options? Should the water company install a separate water line to every home, just to provide dirty, non-potable water? And then every house would have to have additional water lines to each toilet, just to fill them with non-potable water?
The simple answer is: Potable water in toilets is the easiest solution. However, there are people/places/homes that do things a bit differently, like using wastewater from sinks to (at least partially) fill toilets, or even rain-collection cisterns that collect and supply water for toilets. And such things are going to become even more common, in the future, as we continue to overuse supplies of clean water and it becomes less-readily available.
A separate water supply system for toilets would cost too much to build and maintain in a city. The water in it can’t so dirty to cause gunk to deposit in storage tanks, pipes and the toilet, or be toxic for plant life that it can’t be used for watering a garden.
Non-potable water can be used when it’s available, and some toilets have a sink in the top to wash your hands, the water from that is used the next time you flush.
The reason it isn’t used more often is the cost of installing and maintaining all the extra infrastructure. It’s usually cheaper to just increase the capacity of the potable water system to supply both uses. Though places with water scarcity do sometimes have separate infrastructure for reclaimed water.
Because we already have infrastructure in place for bringing clean water to homes.
So why not use it when its already there?
The short answer is that Americans are lazy and our infrastructure was made with potable toilet water in mind. Other countries (and even the U.S. military in some situations) use a three-tier water system. This is especially true in deserts. It does require additional planning during construction or renovation and the storage tanks for grey water, but it is both doable and a good idea. There are even systems that cycle grey water through interior pipe systems to provide insulation in homes, but, again, it’s harder to pull off. But it saves Oh-So-Much on both water and electrical bills…
It’s entirely possible.
It’s currently cheaper to use potable water than to have a system for grey water.
Make of that what you will.
It’s not cost effective. We’d spend more money and time managing extra water systems.
It would be a little more practical to build new homes with a grey water system that is local to that home. So rain water or hand wash basins could be collected to water plants and flush toilets.
There would still be extra maintenance to ensure they remain functional.
Another gain you could make would be to reduce the amount of water being flushed anyway. Older toilets flush way too much water to get the job done..
But again the water, energy and cost involved in replacing the toilets may be greater than saved over the lifetime of the toilet…
It’s probably be more efficient at this stage to improve our ageing water infrastructure and stop leaks. A recent survey found that my local water company lost 58% of the water it put into the system through leakages. Let’s sort that out first, then worry about the small gains from flushing toilets with grey water.
Also stopping single use plastic bottles! You could probably fill a bottle 1000 times over for the cost of a plastic one… Plus that plastic bottle also costs water the make, probably more than it holds.
EDIT: I had a look for stats… Apparently average plastic water bottle takes around 4-5 litres of water to make! So that’s yet another reason to keep with tap water and improve the infrastructure for that.
Same reason there’s a line of 8k pound trucks that were designed to pull a boat idling in the drive thru at Starbucks.
In addition of what’s being said , we could do a lot of things with sea water. It’s basically free, only pumping costs. But salt water is terrible for pipes and maintenance would be cost prohibitive.
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