I was over a friend’s house today, and as usual his dog would run over to the toliet and drink from it about every hour. Now this proves that the water is at least fresh water, but why is it like that. Why can’t we do our thing in salt water? Wouldn’t that lessen the amount of water we waste.
Not Having A Quote Since 1985
That’s a good idea in theory but it would be insanely expensive to pipe in saltwater to all toilets. Saltwater isn’t all that accessible when you live in someplace like Kansas or Colorado.
Well, for one, you’d have to construct two sets of pipes and pumping stations, even if you did live in a coastal area…
FWIW, on Navy ships, they do use seawater, for exactly the reason you state. Fresh water is too valuable to waste in the heads. Also, the distance involved for the pipes is not very great, and there’s plenty of seawater available. 
Not to mention… something as corrosive as saltwater is not the kind of thing you want to pump around.
But I’ll try and make this question a little more sensible:
Why do they use clean water in toilets? Why not waste water from the shower or sinks?
During dry periods at California’s Santa Catalina Island (and there are a lot of them), the public toilets have been altered to use saltwater.
On some ships they use “grey” water, i.e., water that has been used in showers, laundry, or dishwashing. And of course, they have a tertiary piping system to keep fresh, grey, and waste water all separate.
Using grey water in homes wouldn’t be practical. Fresh incoming water is under pressure, so it can be piped to wherever your toilet is. But once water has been used in the shower, laundry, or dishwashing, it’s usually at sewer level and would have to be pumped back up into the house. Plus, having yet another piping system in the house is just inviting the plumber over 50% more.
it’s easier to have a line running into the house for the toilet, as opposed to a storage system/pump for the waste water to be used in the crapper. and you think plumbers make a lot now…
What Fido loves is the coolness as much as the freshness of the water, which is enabled by the nice big ceramic container in which it’s stored. The evaporation of the moisture “sweated” on the bowl’s exterior cools its contents.
(Golly - my first scientific post - I feel positively Cecillian! Now, if you want my ususal self-pitying anecdotal blatherscreet, I’ll tell you exactly what it’s like serving on a ship twelve years past its decommision date with shit, piss and SALTWATER making the heads back up beyond the any Hull Tech’s ability: as the ship rock the flotilla of turds shift from one end of the compartment to the other, and you have to time your dash to the shower stall in between these tides. Oh God, what Ronald Reagan required of us to out-bully Ivan!)
I’ve never heard of gray water being used for toilets in ships. On both aircraft carriers I was on toilets operated with seawater. Fire mains are always charged with seawater so it’s conveneient. Showers may have used semi-filtered gray water but it certainly wasn’t potable.
Padeye - like you I never heard of grey water, just water hours (restriced time for washing & flushing), but have you ever heard of the special configurations they’d sometimes rig on ammunition ships on sub-arctic station? Obviously such a ship could not let the firefighting system be compromised by saltwater corrosion, so they’d connect it to the main steam circut. The only catch was that you’d have to step back before you flushed unless you wanted a plug of live steam on your liberty gear.
Well… first off, salt water would corrode the pipes… second, alot of areas do not have access to it, third, our dog’s/cat’s that drink out of that water would die!
The basic answer is because it’s cheaper to do it that way. If fresh water cost a lot it would be worth going to the expensive of setting up separate systems.
FWIW, a lot of farms that aren’t on the mains water line use double systems like this (at least here in Australia where fresh water is pretty scarce through most of the country). Dam water or bore water is pumped every few days to a holding tank (usually on stilts to give the necessary gravity feed back down to the toilet).
Most places I lived only used that water for toilets, garden watering etc (because bore water tastes like crap and dam water is usually full of sheep shit).
Main problem with the system was that, when the water ran out, somebody had to go out to the dam/bore and turn the pump on and let it run for an hour. If the dam/bore was a mile away and it was the middle of the night or nobody was available you could get a pretty foul build-up in the toilet till somebody got too grossed out and went and turned the pump on.
Yeah Slithy, good thing we didn’t have anything on an aircraft carrier that would burn. Excuse me while I mega-ROFL 
I suppose corrosion in the system is an issue but that’s what hull techs are for. We did have an issue when sprinklers were accidntally turned on in the hangar bay of the Ranger. One of the conflag stations saw smoke from a trash can after a doofus threw a used OBA cannister in. We were in the process of trying to burn the ship down that day and almost succeeded. Bad engineering fire, seven guys killed and a whole engine room burned.
Both carriers had pretty good availability of water so we rarely had shower hours and I don’t recall shower cops with stopwatches. At no time did they prohibit flushing toilets because they were all piped to sea water.
A very good OP question. We (as a society) spend tons of money to make water clean enough to drink and yet most of it is used for things like peeing/pooing, washing clothes, watering the lawn, etc. Very little is actually used for drinking or food prep. It seems that it would make sense to have different grades of water for use.
However, when the infrastructure was set up (piping, pumps, etc.) it was cheaper to have 1 set of pipes coming into a house and 1 set going out.
This cost benefit may soon be outdated as water supplies become insufficient to support growing cities/towns. Of course there’s lots of water in the world, but a particular city/town only has access to a limited quantity/yield…and it’s expensive to bring in new outside sources.
Lately, “sustainable development” is a growing consideration. I know of some new construction projects where it is proposed to collect rainwater from the roofs of large buildings for non-potable use (e.g., toilets, irrigation). There are even ideas such as using perforated/porous asphalt in some areas to promote the recharge of aquifers rather than shunting off all rainwater to the nearest stream.
Among the many “green” architecture strategies used for environmentally sensitive buildings is reusing gray water for toilets. Then it becomes black water (I love euphamistic terms) that has to go to the sewer. FWIW water from the kitchen that contains food is also black water.
Some buildings are doing this now in the US. Not many though because, as Motog pointed out, water is still seen as a “cheap” resource. But 19% of the water used in a residence is for toilets (source) so it is a significant savings. More commonly graywater is used for irrigation (“outside” water use) because it doesn’t require such a complex piping system.
More than you wanted to know about graywater
Pliny Fisk, of the Center for Maximum Potential Building Systems, spoke at Drexel a few years ago about a project they had worked on in a seashore area, and they used the brackish water from about 10 feet down for the sanitary system, because fresh water was too expensive. He found that the el cheapo toilets worked best because they contain no metal components to corrode. So corrosion is a problem, but PVC pipe (yuck) and plastic toilets will fix that.
Phobos points out several other good strategies for general water conservation. Increasing the permeable surface around buildings is one of the most important because much of the rainwater doesn’t make it into the aquifer but instead ends up in the sewer system. Rainwater collection has a high first-cost, but in areas that get enough rain can be very beneficial. Its encouraging that many of these “green” strategies are becoming cost-effective, because that is the biggest barrier to implementation.
Can you tell that this is my thesis topic in Architecture school?