This post is aimed at the longer-term need for purified water. This info is in bits and pieces in the panflu thread but is consolidated here. Check out post 128 there for additional cautions and calculations.
I've gotten cross-trained to work our town's backup wells (which I am confident I could do if there is grid power or fuel for the generator) and purification system (now that one I'm less confident about but I'd give it my best shot). If I learned anything in the process it's how brittle the infrastructure is. Best case scenario if the grid goes down: intermittent supplies of water with uncertain quality (1? hour/day, rotating by sector).
So, even if the water comes out of the tap it will have to be purified. If it's coming from a stream, pond, or lake: obviously ditto. Remember, if the tap water is off or sporadic, the odds are good that the sewage treatment systems are buggered as well. Expect raw sewage, waterfowl feces, and other drek to be in the source water.
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Purification generally requires two steps: filtration to remove larger pathogens (bacteria, protozoa, cryptosporidium, giardia, etc.) and chlorine to kill the viruses that are too small to be removed by the filter. Note that chlorine will not kill giardia and cryptosporidium -- the filtration step is a necessary part of the process.
So, here's my system:
Procedure: use a cheap, effective, ceramic filter (the same type of filters used in Berkely and Katadyn Camp gravity filtration systems) to filter water. Then use chlorine to purify the water of any viruses that have slipped past the filter. Mix the chlorine solution as needed using dry calcium hypochlorite "pool shock."
Pros: Cheap; no fuel consumed; no labor expended in the purification process (once you hump the water); the system is suitable for long-term storage without component degradation; simple, with no moving parts or consumables; large volumes purified quickly (3-4 gallons per hour, faster than a Berkely/Katadyn gravity filter); light weight; very long usage life span.
Cons: a bit bulky (but then this isn't a backpacking system).
System Components
- Two Rubbermaid "Keepers Rough Tote" 18 gallon size. Around here these are blue or gray in color and semi-rigid. Don't get the clear ones, the plastic is too brittle. In a pinch, any container large enough to hold the ceramic filter will do. These are $3.97 apiece at Lowes right now.
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- At least 500 coffee filters from a big-box store, 1000 isn't out of the question. Get the biggest ones you can find. They're cheap.
- One "style A" filter system from Pure Water Products with a Doulton Super Sterasyl cartridge. $45
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- Strictly Optional: One charcoal filter for each 500 gallons purified plus adapter: Omnipure filter + adapter from Pure Water Products. $22 ($15 per additional filter, the adapter is reusable). Here's the setup w/ the charcoal filter:
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- One pound HTH® SUPER SOCK IT Shock 'N Swim 60% free chlorine by weight. (Be careful, you'll find 45% and 50% available chlorine formulations by the same manufacturer as well -- you don't want those.) This will handle 65,000 gallons of water. $2.99
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- One plastic teaspoon.
- One 1.5 ounce shot glass, preferably glass or plastic.
- One 2 gallon container (or just a big plastic container to mix your sanitizing solution and two old one-gallon bleach containers and a funnel to fill them, that's what I ended up doing in my test run).
- One large plastic measuring container (I used a clean 5-gallon bucket with volume marks)
- Battery powered clock (you'll need this for many things if the grid is down)
- One of those plastic "tuff-scrub" sponge-shaped thingies from the dishwashing products aisle.
Procedure
1. Mix up a batch of stock sanitizing solution using the 60% pool shock and water: add one heaping teaspoon to a measured two gallons of water in the clean bucket. Mix until dissolved. Use the funnel to fill the two empty bleach containers. This 2 gallons of 0.86% free chlorine is your stock sanitizing solution. DO NOT DRINK IT. (Add one 1.5 ounce shot glass of this solution to each gallon of impure water and wait 30 minutes.)
2. Put one Tupperware tub on a table top. Lay the assembled ceramic filter (with delivered elbow fitting and plastic tubing attached per instructions) on it's side in the tub. Keep the open end of the tube outside the tub - do not contaminate it with dirty water. Measure whole gallons of dirty water into the tub, one at a time, until the water is only deep enough to cover the filter.
3. Now add one 1.5 ounce shotglass of stock sanitizing solution for each gallon of water you added in step 2. The filter needs to soak the first time you use it. Put a dinner plate or something over it to hold it under the water and let it soak until it doesn't float any more. I suggest you soak it overnight the first time you use it.
(Next day or several hours later when the filter no longer floats)
4. Put the second tub on the floor under the table. Get the free end of the tube attached to the filter in the top tub and suck on it like a straw until you get water (This is why we disinfected the water in the top tub -- you are getting it in your mouth in this step. From now on we'll disinfect after filtering.) Quickly drop the end of the tube into the clean lower tub. You should have started a siphon and the water should continue to flow. If not, try again. If you can't suck any water or the siphon won't stay going you either have an air leak in the system or the filter wasn't soaked long enough.
5. Fill the top tub with more dirty water. Do not disinfect this water (do not add more stock sanitizing solution). Let a full tub go through the filter.
6. When the bottom tub is full, add one shot glass of sanitizing solution to the tub for each gallon it contains. (Yes, we're overdosing a bit as some of the water was already treated in the top tub -- just do it.)
7. Wait 30 minutes and then throw the water out. Yes, that's right, toss it. The first batch is full of ceramic dust from the filter and needs to go. We disinfected it to keep the bottom tub clean.
8. Add more dirty water to the top tub. The directions said adding water to the top tub would re-start the siphon even if it had run dry and to my surprise they were right. When the bottom tub is filled, add one shotglass of stock sanitizing solution per gallon and wait 30 minutes until using.
Notes: During a filtering run, my plan is to keep the top tub continually filled with dirty water and keep filling Tupperware tubs until I fill four tubs or run out of water (the tubs have tight-fitting lids). But then I have a large supply of water on hand. YMMV.
18 gallons makes for one heavy tub. Put it where you want it and then fill it.
Measure 18 gallons into one of your tubs one gallon at a time and mark the fill line each time. You can repeat the process for each tub or transfer the marks using a rule. You need to know the correct volume to get the right dose of stock solution added.
If the dirty water is particularly nasty, let the particulates settle out before filtering to preserve the filter's life. Or, use the coffee filters to pre-filter the dirty water before you put it in the top tub. You'll have to jerry-rig a container to hold the filter.
If the ceramic filter slows, use the "tuff-scrub" plastic pad to scrub the exterior. This won't hurt the filter and will restore its flow rate.
You can avoid rigamarole if you prep the filter NOW using clean tap water with the proper amount of chlorine solution added (you can use unscented household bleach if you don't want to crack open a pack of pool shock, check the Clorox web site for drops/gal). After soaking the filter and runing a tub of water through it, seal the filter into a Ziplok bag and it will be ready for use. I'll probably run chlorinated water through it every 4-6 months just in case.
Addendum: I use the setup with the charcoal filter cartridge in-line with the ceramic candle. This adds a couple of feet's worth of tubing to the system. If you don't choose to use the charcoal filter your tubing attached to your filter may be too short to extend up the side of the top tub and then down into the bottom tub. You can easily extend the tube length using additional tubing from the hardware store --1/4 inch tubing is a standard size for refrigerator water systems. Get a straight fitting for hooking two lengths together. Whole thing'll cost 3 bucks. TEST YOUR SYSTEM OUT BEFORE YOU NEED IT!