Don't put a garden hose in your pool

[snopes]

Comment: Leaving a turned off hose in a swimming pool will contaminate
the house's water lines and perhaps the whole neighborhood. This was an
explanation for using an anti-siphon valve. Is this possible? Since the
the hose is turned off at the faucet, water shouldn't be able to be sucked
up into the home, and, therefore, cannot fill the pool either?

[LittleDuck]

Um, we always did this. We were in more danger from this town's woeful water supply than the pool water. Just as the comment says, the water cannot go back into the pipes. The worst is that any water left in the hose may get stagnant in the hose (horrors!) or leak out the end (no, not that!). The act of turning the faucet off is like shutting a door. Nothing can get out and nothing can get in either.

[hambubba]

EPA information on preventing cross-connection of drinking water sources.

My first inclination was to scoff. But, I googled "garden hose pool" and this subject came up. It is a potentially serious problem.

ETA: Of course, this IS only a problem in the OP IF the faucet is left on.

[DaGuyWitBluGlasses]

If its left on: the pressure from the depth of pool is no comparison for the pressure in your water supply:

(Since nobody has pools that are as deep as the Water Tower is tall.)

[hambubba]

The exception here is when you have backflow; such as from a pump failure. In a gravity-fed, water tower supply, that isn't an issue normally. However, say a system is under pressure, and a pipe breaks. The pressure release will cause flow toward the leak, and yes, it can "suck the water out of the pool".

Rare, yes. But possible.

[DaGuyWitBluGlasses]

I would think any pipe break or plumbing job is a contamination risk of itself, and things would need to be flushed out regardless of whether there's an open hose or not.

[Keeper of the Mad Bunnies]

Health codes are always created with the 'worse case scenario' in mind. It is unlikely that a problem would occur as the result of leaving a hose in the pool, but it is not impossible.

Valves fail, so a shut off faucet does not mean water cannot leak backwards. You are also not seeing the possibility of a failure within the house's water supply. That is the more likely scenario which could result in a backflow into the potable water supply. It would affect only that house (and most homeowners may not be aware of what happened and think to properly flush all of the lines).

Some outside faucets feed directly from the house main. In those instances, a pressure failure in the municipal system, along with a failure at the faucet, could result in the contamination of the municipal supply.

Of course, one could ask just how dangerous pool water is anyway? If the pool is properly maintained, it can probably be considered 'potable' and there would be no real contamination.

(ETA) - You do not need a complete failure of the water system. All you need is a reduction in the pressure large enough to allow backflow. A fire in the area can cause a reduction in the municipal pressure, as can a lot of people using water at once. Pressure is also affected by how far the location is from the last pumping station.

(Why, yes. Health officials do think about all of these contingencies!)

James Powell

[Open Mike Night]

Actually happens more often than you think.

Part of the joy of my job is that I have to be a certified municipal water supply operator.

The problem is more prevalent if you have your own well, but it happens in municipal supplies also. Leaving the hose in the pool may not be the biggest problem, since the water is most likely chlorinated. Although, if the chlorine concentration is "hot" enough, it will corrode your pipes and your well pump parts.

The real issue is laying your hose on the ground, in a bucket or in a slop sink when it is not running. these are notorious germ factories, and fun critters like coliform bacteria will work it's way up the water in the hose all the way to the faucet. Then it only takes a very small backflow hiccup to pull the bacteria to the inside piping, where it multiples and contaminates the system.

This is also the reason alot of health departments don't allow the old "frost free" faucets anymore, since they tend to create a backflow on their own.

Originally Posted by Open Mike Night

Actually happens more often than you think.
This is also the reason alot of health departments don't allow the old "frost free" faucets anymore, since they tend to create a backflow on their own.

Interesting, Tell me more about the old "frost free" faucet. How did they work?

[Open Mike Night]

Originally Posted by Kennicott

Interesting, Tell me more about the old "frost free" faucet. How did they work?

The old style of frost free valves have the water line below the frost level. there is a riser that comes up out of the ground to a hanlde type shutoff. When you close the handle, the valve turns the water off below the frost line, the the water in the riser drains out (creating a backflow) so that there is no water in the pipe above the frost line. They're more common on old farms.

I see. Thanks. I never thought of that before. Here in Alaska we don’t have many outdoor swimming pools but we do have a lot of wells. I can see how a well could become contaminated easily without check valves.

In the rural areas, where the frost line gets down quite a ways, people have problems with freezing lines. They use a pitless adapter in the well casing, usually putting it down ten feet or so, this eliminates having to run the line from the pump at the bottom of the well up and over the top of the casing. If you do that then you have to have a heated shed or something over the top of the casing. Trouble is that the water in the line sometimes freezes even when everything is down deep, so a lot of folks drill a small hole in the riser pressure line just above the pump. A one-way valve on the inlet side of pressure tank in the house prevents the domestic water from the house siphoning back into the well. The small hole doesn’t reduce the pressure from the pump by any significant amount. I wonder if this lash up is up to code.

Another domestic water contamination problem is possible where one puts antifreeze in the boiler, if the house should freeze up then all the heating radiators and pipes don’t rupture. Most hot water heating systems are connected to the fresh water supply line, so if the boiler pressure gets too low a little water is added. But if the domestic water pressure goes down the glycol from the boiler could feed back into the fresh water supply. I put antifreeze in my system once and had dual check valves but hearing what happened to people who drank glycol for booze gave me nightmares, so I drained the system and went back to plain water.

[DesertRat]

You know... this is something of a useless post, yes, but I just wanted to share that threads like this are why I love this site. I've learned some pretty damned fascinating stuff here.