Remaining "flush" during the Zombie Apocalypse
March 1, 2014 12:03 PM   Subscribe

Not that I'm writing a Walking Dead fan fiction or anything, but if I was I have a few hypothetical questions about water towers, wells and human waste disposal during an extended power outage.

I'd appreciate it if someone could explain water towers, gravity wells and the like to me in simple terms (unlike the extremely technical discussions I've found via Google). Suppose the electricity has been out for one year. Water towers work via gravity, right? As far as dispensing stored water, that is. Do they require some sort of electric pump to replenish the water? Suppose a small area, like a prison, has its own water tower - would the back-up generator that supplies electricity to the gates and lights also power the pumps connected to the water tower? (The back-up generator runs on diesel fuel, so the survivors are eventually able run it on used the abundance of cooking oil scavenged from fast food restaurants.)

What about wells - both gravity and artesian - on private property? How long would they continue to provide water to a house (or an outdoor hand pump) without any electricity? (I'm not worried about potability; let's presume our staunch survivors are always boiling any water they use for drinking or cooking.) And if either/or the water towers and wells continue to provide enough water for the sink taps, showers and toilets for an extended period of time, is it safe to keep using flush toilets when the traditional sewage treatment plants aren't functional? Or don't such plants require electricity? Is there a point where using either a homemade composting toilet or The Great Outdoors in general is inevitable when it comes to answer Nature's call?
posted by Oriole Adams to Science & Nature (10 answers total) 7 users marked this as a favorite
I thought about this a little when 1999 was wrapping up. I lived in a rural house with a gravity-fed well. The water came into the house because the well was higher on the land than the house was. There was no pump. It worked in a power outage and would have worked in an extended power outage. The same was true for the septic system, more or less. Ideally these systems work with a minimum of intervention, but realistically people come and pump the sewage out of it every so often. This is conceivably something that could happen with hand pumps. If you're septic-curious, this book explains the ins and outs of this sort of system. Don't know much about water towers but I will note that composting toilets often have fans as part of the whole system, so these would have to run differently than usual.
posted by jessamyn at 12:10 PM on March 1, 2014 [1 favorite]

is it safe to keep using flush toilets when the traditional sewage treatment plants aren't functional?

My guess is: yes, probably. For toilets whose plumbing is hooked to a municipal sewer system instead of a septic tank. Because you have to figure that a zombie apocalypse is going to greatly reduce the number of people pooping into that system -- the water treatment plant itself will cease to function, but the volume of the waste stream has been so drastically reduced that the sewer system itself becomes a giant midden, with plenty capacity to hold what little waste it receives.

This also depends, of course, on WHERE in the system the toilet in question is located. It could be on the wrong side of a now-defunct grinder pump (used to pulp waste for easier processing through inclined or smaller-diameter sewer lines), while an identical toilet across the street would be on the other side of the juncture and thus ok to use.

Septic tank systems may not require power and given functional field lines and land that percolates may work for years or even decades without a problem. But then again, they may not. It all depends on the state in which they were left when the zombie plague hit.

One of the interesting things to me about a zombie apocalypse is how rapidly gray-water re-use systems would catch on among surviving communities. Capture > Boil > Primary Use > Catchment > Secondary Use > Catchment > Waste Disposal > Discharge.
posted by BitterOldPunk at 12:39 PM on March 1, 2014 [1 favorite]

Sewers predate water treatment plants by hundreds or even thousands of years. As a toilet has to be within easy walking distance of its users, the main job of a sewer is really about taking waste away from where people live. Treatment plants are about cleaning the disposed water to the point where letting it into the environment (or back into use) no longer poses a threat to human health or nature. Letting your dirty water float off down the river or into the sea might not be a major concern in a survival situation, the moreso if you can be sure that there's no flowback or seeping into where you source your water.

That said, modern sewer systems often do rely on pumps to shift waste about, so the dirty water might find an overflow outlet in places it ordinarily wouldn't.
posted by Thing at 12:59 PM on March 1, 2014

is it safe to keep using flush toilets when the traditional sewage treatment plants aren't functional?

It's safe for the user, and assuming it is a gravity sewer system with no pumps in the line, it will continue to flow until there is a blockage somewhere. Given that most sewage treatment plants need electricity, they'll either block up or go into bypass operation (like what happens in places with combined storm and sanitary sewers when it rains hard) -- in either case, zombies or human survivors drinking downstream are going to be at somewhat higher risk of fecal contamination.

Old-style septic systems don't need electricity but will eventually need to be emptied of sludge. Normally that's done with a pumper truck but if the tank had adequate sized openings, you could climb in there and empty it by hand. Some modern septic systems designed for high groundwater or impervious soils do require electricity though. If you had no concern for downstream users you could simply pipe your sewage into a nearby stream or drainage ditch, of course.

City water will often be gravity-fed from water tanks or reservoirs, but usually the water needs to be pumped into those. I am sure there are cities with purely gravity systems that would keep functioning indefinitely until there was an eventual clog or pipe break.

Some house wells can be gravity-fed (often from a springhouse higher up on a hillside) or from artesian wells (where the water comes out of the ground under its own pressure) -- either of those would keep functioning indefinitely, assuming minimal maintenance to repair the pipes, etc. But the vast majority of modern household wells rely on an electric pump down in the well and will not function without a source of power. Those well casings are small -- six or eight inches often -- so it would be difficult or impossible to convert it to use with a rope and bucket.

Digging a well by hand can be easy or virtually impossible, depending on how deep it is to groundwater. Anywhere you see houses that predate electricity, there is probably easily-sourced water (streams or shallow wells) because they needed to drink and wash clothes just like your survivors will, but with modern drilling technology it is easy (though not cheap) to drill hundreds of feet down for water. An old farmhouse may still even have a springhouse or a well in one of the outbuildings, for example.

If water is hard to access (hauled by hand from the river, pulled up in a bucket from a well, or stored rainwater in barrels), flushing toilets is going to seem like a huge waste of water and instead an outhouse or a composting toilet is going to look like a great idea.
posted by Dip Flash at 1:17 PM on March 1, 2014 [2 favorites]

I'll just chip in that you can flush toilets with a bucket of rain or gray-water. Just slosh it into the bowl until it starts to flush.
posted by codswallop at 1:58 PM on March 1, 2014

Regarding composting toilet fans - if the air vent pipe is painted black and rises high enough above the level of the roof, the heating of the pipe by the sun will cause an upward air flow naturally without an electric fan. Alternatively, if a tall black pipe is not feasible, a tiny solar panel connected to the fan will also work.
posted by Kerasia at 2:18 PM on March 1, 2014 [1 favorite]

I work in home construction.

The water in a water tower on top of building is basically standing water, being used to create pressure on the plumbing pipes in the building and help prevent air pockets in the pipes. New potable water is pumped into the building by the public utility (the water company). If the water company's pumps went down, the city would go dry, the building would drain a water tower in no time flat. In fact, in most buildings, the water in the building's water tower would back-flow out of the building, into the newly empty water main pipe (the water company's pipe) running down the street.

If the water is out, you can not use the toilet. Water is needed to "flush" the waste into the sewer. Without out some sort of liquid to flush, the waste would build up in the bowl. Your toilet is currently connected to water from the public utility, and that water is used to flush. However, any water can be used. [Home experiment: Fill a 2 gallon bucket of water, and pour it fast into your toilet bowl - if you have never done this before, it is a little scary at first, because it seems the toilet will over-flow, and you will make a mess - but that is not what happens - pour the water in, and toilet flushes itself.] Any dirty water source and a bucket could be used to flush a toilet, and keep it working.

All wells use electricity today. (Either that, or you have to manually lower a bucket into the well). However, solar well pumps are becoming increasingly common. Especially in rural and agricultural areas. You could have potable water forever, living off the grid with one of these. Pump your water into a tower above the house during the day, empty the tower at night, re-pump in the morning. Keep a week supply of water in your tower, in case of cloudy days.
posted by Flood at 4:37 PM on March 1, 2014

The tall water towers that are found in smaller towns are storage facilities. There will be pressure in the homes they serve, without the need for any electricity or other energy, so long as they are filled with water. The hydraulic pressure based on the large volume can keep pressure sustained for a long time when transmitted to small-caliber pipes.

But electricity is needed to operate the pumps that get the water up to the water tower to begin with. Gravity and water are ineluctable.
posted by megatherium at 7:00 PM on March 1, 2014

You don't have to pour water into the bowel to flush, you just need a full tank. It is way easier to just pour that two gallons into the tank and then flush the toilet conventionally.

And all municipal sewer system have a 'fail-dirty' gravity overflow in place in case of power failure where the pump stations and treatment plant will overflow into whatever discharge point is nearby. This is to protect the pipe systems from surcharging and 'bursting' at the seams causing permanent leaks and also to keep peoples homes clear of sewage backup. It is sort of the like the overflow port in sinks and bathtubs. BTW if this every happens it is a really BIG DEAL and the EPA paperwork is really a mess (as well as your local river/wash/ocean).
posted by bartonlong at 9:06 PM on March 1, 2014

Oriole Adams: "What about wells - both gravity and artesian - on private property? How long would they continue to provide water to a house (or an outdoor hand pump) without any electricity?"

The old style windmill with dozens of blades that was so common in rural areas a 100 years ago was for pumping water not generating electricity (their high torque, low speed design is good for water pumping but inappropriate for electrical generation). Those would keep working as long as you had wind and I think the rural location in season two had one of those windmills. Also any time you have flowing water you can rig some sort of pump. A ram pump for example only has two simple moving parts and is powered by the water flowing through it. And there are lots of deep well hand pump designs that anyone with access to a building supply borg or farm supply could construct from parts. If there is a well already bored you would be able to get the water out.

Waste most places is going to be as simple as digging a hole; outhouses were the norm in rural areas across North America until quite recently.
posted by Mitheral at 4:37 AM on March 2, 2014 [1 favorite]

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