Drinking rainwater

Thought I'd start a thread with info on drinking rainwater.

one of the highest quality water sources out there. much better than groundwater if collected and stored properly.

upwind contaminant sources: not collected directly downwind from industrial pollution sources...it's not the rain, it's the air that is contaminated...we're breathing this anyway...
clean surface: metal, slate, bamboo, glass are preferred, can also use clay...other catchment materials?
contaminant exclusion: First flush filters and screens http://en.wikipedia.org/wiki/First_flush_device http://rainharvesting.com.au/products/pre-filtration/first-flush-water-diverter http://www.eco-web.com/edi/02431.html also, clean gutters via maintenance or leaf screens are beneficial
non-leaching tank with biofilm: Non-leaching tanks include Polyethylene, ferrocement, stone (of certain types), metal (usually aluminum or galvanized steel) A major portion of non-leaching is the development of a biofilm usually including algae, this means the inside of the tank needs some access to sunlight to grow photosynthetic algae
screened openings: prevent rodents and insects from getting into the system
elevated outlet pipe: needs to be 3" minimum above bottom of tank to avoid disturbing the settled sediment and biofilm
pH management: pH needs to be above 6.0, ideally 7-8. use limestone or marble chips since rainwater is naturally about 5-6. keeping the pH above 5.5 ensures heavy metals are not dissolved. above 8 insures few, if any pathogenic bacteria can grow.
I need to find some more detailed references on this, but for now http://www.who.int/water_sanitation_health/dwq/gdwq3rev/en/
overflow/airvent: can be the same or two different components: screened.

Some of my favorite resources on rainwater collection and drinking using tanks

OAEC Water Institute: http://www.oaecwater.org/publications

review of a decade of rainwater harvesting research: http://www.hydropolis.com.au/Papers/SIA_Coombes1.pdf Awesome! includes info and data on the "treatment train effect"

that's a good start i think

I was throwing around the idea a little while back on making a passive solar distiller for water purposes. The filtration steps played into my thought stream, and I was kind of jumping back and forth from the regular solar hot water heater design with a condensing apparatus, and a collection flask heated by a concave mirror. This wouldn't have massive output, but I thought it seemed like a cool project. Your thoughts?

Adam Poddepie wrote:I was throwing around the idea a little while back on making a passive solar distiller for water purposes. The filtration steps played into my thought stream, and I was kind of jumping back and forth from the regular solar hot water heater design with a condensing apparatus, and a collection flask heated by a concave mirror. This wouldn't have massive output, but I thought it seemed like a cool project. Your thoughts?

I think solar distillation is a great option for water purification. That is how the water vapor that condensed to form rainwater is made from the ocean and lakes. Rainwater is made in other ways as well (i.e. transpiration, wind evaporation, snow sublimation).

My first questions would be why are you distilling water? and likely this will be specific to your water source: is it a chemical contaminant, a biological contaminant, or both?

biological you can just heat it to sterilize it. this can be done in a jar painted black on the outside with a wax thermometer inside that melts when you get it hot enough. I think 180 F should be enough, 200 F will sterilize more quickly, be careful if you get over that temp since water boils at 212 F.

chemical, you would want to distill or filter some other way. slow sand filters and charcoal filters work well and are often gravity powered. solar distillation would work as well.

the issue with a solar distillation apparatus is that you still have a collection surface that needs to be clean. if you have this, then you should be ready to go. you can always do a before and after test to be sure.

specifics to look at are similar to water catchment planning: quantity of storage, quantity, rate and timing of supply, timing between periods of supply, quantity and rate of use, contaminant sources

both options you suggest sound workable. something as simple as a piece of sheet metal places to heat with the sun and bent to channel water into a flask can work if you have humidity to condense.

not sure if I answered your questions. let me know

You make very valid points, and they are all things that I've thought about as well. It really ends up boiling down to my love of tinkering. I know there are other simpler ways to sanitize water, but a solar still just seems like a fun project. The major problem with my designs is the rate at which it supplies water. Even in the best of circumstances it probably wouldn't be enough water for a family without having to make an extremely large apparatus.

You sheet metal idea seems interesting, the rate at which water is distilled will depend on the area of the plate, the ambient temperature, and amount of sunlight gathered.

If all else fails, it'd be fun to gather the water I use to brew beer in this fashion. Probably make for some clever beverage names.

you can always use a similar apparatus to distill other compounds from alcohol to essential oils. you can get as complicated as you want designing separating columns and chambers at different temps. if you love tinkering, there might be some good business products to be invented along this line of solar energy use.

also for a great solar tinkering site, check out http://www.builditsolar.com/

for other condensation techniques, check out Brad Lancaster's site http://www.harvestingrainwater.com/condensate-harvesting/

I'm sure there's lots more info on these two threads (solar distillation (aka evaporative condensate filtration) and ambient condensation harvesting). perhaps we can start threads for each here on Permies.com to try and collect and organize that info.

That sounds like a good plan. Using multiple distillation risers would make for some interesting uses. It'd be even better if it was modular so you can vary the number of distillation chambers based on if you're only trying to purify water, or if you're going the full mile and need chemical grade alcohol for cleaning (I believe for non-consumption that's legal).

I hadn't thought about harvesting oils, but that's definitely something I'd be interested in. Oils are so widely useful, and they're always so darned expensive on store shelves. Probably make a nice item for local markets too if it comes down to it. Thanks for the info.

I have been thinking about the pH in my rainwater. Anybody have a good technique for raising the pH of their rainwater?

Is there a substrate that I could dump into my two 1700 gallon tanks to do this in a low tech way? Dont really want to use a chemical pump or a backflush media filter for reasons of cost and simplicity.

thanks in advance---

Adam Klaus wrote:I have been thinking about the pH in my rainwater. Anybody have a good technique for raising the pH of their rainwater?

Is there a substrate that I could dump into my two 1700 gallon tanks to do this in a low tech way? Dont really want to use a chemical pump or a backflush media filter for reasons of cost and simplicity.

thanks in advance---

Limestone or marble chips. Better yet, build a gravel filter to stick between your downspout and your tank and fill it with marble chips or crushed limestone. The limestone, being more porous, will have more of an effect, but if you get too much dissolving and hardening the water, marble will have a less pronounced effect on the water.

thanks for the quick reply John,
if I were to just dump some chips in the tanks, how much would you reccomend?
I could also make a wire basket of sorts, fill it with the chips, and have the water pass through that in my downspouts. This would use much less material but the water would have a more dynamic contact with the material.
Any ideas for sourcing?
thanks-

Adam Klaus wrote:thanks for the quick reply John,
if I were to just dump some chips in the tanks, how much would you reccomend?
I could also make a wire basket of sorts, fill it with the chips, and have the water pass through that in my downspouts. This would use much less material but the water would have a more dynamic contact with the material.
Any ideas for sourcing?
thanks-

You're welcome, Adam. I lived too long in a hard water area to recommend dumping it in the tank. You don't want water that is saturated with dissolved limestone and leaving little cave formations wherever it dries up. If you can do the downspout thing, or even screen off the downspout and leave the marble gravel in the gutters, that might be the best way.

You can usually find white marble gravel in home improvement stores or landscape places that sell it by the cubic yard. When I moved into my house, the previous owners had one flower bed where they had put down white marble gravel. Sure can't find that stuff in this soil, so it had to come from somewhere.