Last week I published some thoughts about emergency water supplies, in the wake of Hurricanes Harvey and Irma.
Now Accuweather has put up two interesting articles dealing with the threat from contaminated water following a hurricane, and how to deal with the problem.
I highly recommend reading both articles, as well as my earlier article and a longer one that I wrote on the same subject some years before. Many people put some effort into storing emergency food supplies, but pay little or no attention to their need for water, keeping only a few flats of 16-20 ounce bottles of water on hand. That may supply drinking water for a few days, but it won’t be enough for cooking, personal hygiene, etc.
Furthermore, I’m hearing many reports from survivors of both Hurricanes Harvey and Irma that sewer lines ‘backwashed’, flooding bathrooms (if not entire homes) with the contents of sewers pushed back up into toilets, baths and basins by overflowing storm water. This is particularly problematic if you plan to fill your bath in an emergency, to use it as a water reserve. Even the smallest backflow will ruin that water. As the old saying goes, “If you add a glass of wine to a barrel of sewage, you have a barrel of sewage. If you add a glass of sewage to a barrel of wine, you have a barrel of sewage!” What’s more, any sewer backflow that overflows your toilet(s), basin(s), bath(s) or shower(s) will cause a major contamination problem, one that will probably require (expensive) professional attention to clean up.
It begins to look more and more desirable to install a sewer backflow valve to prevent this problem, particularly in flood-prone areas. FEMA has instructions on how to do that (link is to an Adobe Acrobat file in .PDF format). Even though we don’t live in a flood-prone area, I’m going to look into that as part of our next residential upgrade.
Peter
99% of all water districts/sewer authorities require a sewer backflow valve on all new construction and all remodels, has been so for the past 20 years. Enforcement is low however.
I live in pueblo, and you have to have back flow devices or your plumbing ground work won't pass inspection for building dept. Also keep in mind the flapper valve will be the first thing to plug up if stuff that shouldn't be in sewer get flushed.
For a first approximation sandbagging the toilet can help. Many other drains are enough higher to make a difference though nothing to count on.
I used to be a reporter whose beat included the local sanitation district. Their attitude was that everything between the sewer pipe and the (in this case) household plumbing fixtures was the property owner's problem. So a backup into your house was your problem. They recommended having those valves.
One of these screwed into your clean-out pipe can save the day, your health department may not like it though:
https://www.amazon.com/Homesaver-Flip-Sewer-Relief-Valve/dp/B00PZLP1J4
The automatic backflow prevention valves, like this flap one aren't bad but I'd hate to trust one since they depend on being reasonably clean to seal well:
https://www.amazon.com/Oatey-43904-Backwater-Valve-4-Inch/dp/B000BQSFJ6
If you know trouble is coming a manual gate valve like this is better protection:
https://www.amazon.com/SCH-80-PVC-GATE-VALVE/dp/B018H64JGE/ref=pd_sbs_60_14
These links are just the first ones I found of the type, not recommendations, shop carefully!
Plumbing systems need DVW (drain-vent-waste) venting to allow air into the system so it drains properly; I wonder if it's possible to incorporate some physics into the system to allow backflows out through the DVW venting instead of the fixtures.
Figuring the gravity head on a napkin, it's obvious there's less resistance available from the sink and toilet traps than in the footage to a roof vent, meaning the path of least resistance will be all over your floors.
The "easy way" would be connection to the public system through a sewage pump because those could be – and I say "could be" reservedly – because the pumps routinely incorporate some degree of backflow control. Whether it's enough, I dunno, and just having a pump adds complications, maintenance, breakdowns and requiring power to work being at the top of the list.