For a re-roofing or new build, I was pondering the possibility of capturing and purifying water for drinking use. Are there good examples of this? What roofing materials should be used or avoided?
This could be relaxed to vegetable gardening gray water, so long as the roofing material didn't introduce something that would end up in the produce (unless it was practical to filter out before reaching the produce).
It turns out people have consumed rainwater for millions of years. So there's some precedent.
This is very well covered online, so grab a search engine and get reading. Here's a summary of concerns.
In the US, it may be illegal (look up "water rights") but for individual home use, that is usually ignored.
You'll get a lot of water from your roof really fast. It's pretty amazing.
The biggest problem is the dirt on your roof. The rainwater coming down is great, but once it hits your roof, it's dirty. You can redirect the first bit of rain, and then collect once the roof is clean(ish).
The roof material matters. Some roofs will leach small amounts of toxins in to the water that you probably don't want to drink. Metal is probably the best choice for a roofing material.
For most homes, only a small portion of the water goes to drinking. Much of it goes to laundry and flushing toilets and irrigation. These systems don't mind slightly dirty water (including greywater). Use your collected rainwater there first. You can haul it by bucket or plumb something special.
A problem specific to collecting rainwater for irrigation is that it always comes at the wrong time. You would have to save it from the wet season to use in the dry season, which implies a huge cistern. Being clever helps. For example, a cistern can go under a deck.
Any water storage should be protected against mosquitoes. You can put fine mesh screens over openings, or (my favorite) put goldfish in the tanks to eat the larvae.
Cleaning dirty water to be drinkable is harder. If you build a complex filtration system, you'll probably negate all the financial and ecological benefits of saving that small amount of water you were drinking. My favorite approach is the slow sand filter - it's simple, cheap, low energy, but it takes a lot of work. read here: http://www.homestead.org/TedPraast/SandFilter/Filter.htm
As I mentioned in a comment to Jay's post, rainwater collecting may be illegal, dependent on your State. Western states, which get less rain, generally employ the doctrine of "prior appropriation"; an entity can claim the rights to water that will enter a waterway even if it hasn't arrived there yet. This means that by collecting rainwater into a cistern, and thus preventing it entering a stream, lake or aquifer, you have prevented the claimant from receiving the water they were promised by their permit and are breaking the law.
The dividing line between states that do and don't employ this doctrine is generally the Rocky Mountains, though a few Plains states prohibit artificial collection of rainwater without a permit. Most Eastern states have more "riparian" doctrines (you are free to access any water that falls on, collects on, borders or passes by your property), with more or less restriction based on type and amount of use and current drought conditions.
In Ohio, rainwater catchment is legal; however, catchment and cistern design and construction is among the most highly-regulated of all States, and while you don't need a water use permit, the catchment system must be permitted by the health department. Have a look-see: http://www.harvesth2o.com/statues_regulations.shtml#oh
Once you've sorted out the legality, Jay's post has the rest of the basics.
While researching, I looked into the laws of my own state and found some pretty interesting facts, which may be entertaining to other readers:
Texas has mostly "prior appropriation" doctrines for surface and groundwater; all major waterways within the borders of the State are owned by the State and administered "for the public good", and it's illegal to divert these waters without a permit. Despite that, an older, more riparian doctrine has persisted with regard to rainwater (called "diffused surface water" in the statutes); landowners may collect precipitation that falls on their property and hold it for domestic and livestock use without any permit, provided you don't have storage capacity in excess of 200 acre-feet.
Trivia time:
The limit is thus something the average homeowner NEVER has to worry about. Catch as much as you can in Texas.
A good example is the roofs in Bermuda. If you search for 'rain collecting in Bermuda' you'll find lots of examples. Here's one:
Alright, so assuming it is not illegal for you to collect rainwater (and even if it is...) and assuming you have a gutter system, why not just redirect your gutter system in a catchment system, or even a few catchment systems. This guy has done something similar here: http://www.instructables.com/id/Need-Free-Water%3f--Build-a-Rain-Barrel/
Next you have to tackle the issue of drink-ability as this is simply collecting greywater. You could add a filtration system in, there is an example of that here: http://www.instructables.com/id/Rain-water-collection-filtration-storage-syste/ Although a filter to catch any dirt and foreign objects and some treatment chemicals should do the trick.
Another option I was toying with is an evaporation system. I am not too sure how well it would work though. Essentially what you could do is have the rain water go into a inner barrel that is contained in a larger barrel, then by putting a cone on top the water would evaporate onto the cone, roll down, and fall into the large barrel, a small tap on the side of the large barrel and you'd be ready to role! Of course it would have to be in a sunny area for this to work well.
Another option would be to simply filter out any contaminants and then boil the water, although then the water is less readily available as you have to boil it. It also is less automated.
Yes, rain water is perfectly safe for drinking purpose and qualifies all WHO tests till the time it hits your rooftop where it interacts with the dirt stored there. However, still this water can be used if the first flush of water is diverted from the roof tops. It is estimated that during a storm first 10 minutes of roof top water from a CGI sheet will carry the dirt and remains of the birds and later part of the storm water will be clean and safe for drinking. This clean drinking water can be stored in the water tank for many days, however at an average of after 20 days, you are required to add chlorine for disinfection of bacteria.
