I've gone and promised someone that I'd pull all the info on this project together so others can duplicate it more easily, and perhaps avoid some of the mistakes I made along the way. This one's been real important to me personally, as I'm almost fully off-grid and a well would have required various permits and a ton of money upfront I had other uses for - and I still have other uses for the money I'm saving in property taxes. Not having a well, or grid power makes all my campus essentially an undeveloped piece of land in the eyes of the tax people and while difficult to accomplish - hey, challenge accepted! Consider the yearly savings on 40+ acres and 4 buildings vs the tax burden of "nature preserve" and a lot of decisions I've made here make a lot more fiscal sense than some would have you believe. The difference has paid for the fusor project, most of these buildings...and not having to have a "Real job" since I was ~ 45 (20 years early "retirement").
Water is a biggie. I'm lucky to live (well, I did chose where to move to) in a place with more than adequate rainfall, and where the air is now pretty pure, so the water is pretty good. Wasn't always that way, but about the one major good thing the EPA did was shut down dirty coal plants west of me that were making the rain have the pH of lemon juice... After living here for awhile, you can smell a city or big town from miles away - that's some pure air you get used to.
Ok, that's the upfront line. Now for the real stuff.
Here's a block diagram overview. Sorry for my sloppy drawing/writing skilz..I hope it's kinda obvious from the rest.
Collecting rain is theoretically trivial, but actually quite a trick if you want to use the water. Rain isn't pure already, and the collection surface - here a roof and solar panels, gets dirty with anything airborne - pollen is one of the worst, but tree seeds, leaves, bugs living and dead, little rocks from the shingles...you name it, also comes down, and sometimes it's so nasty that you'd not even want to clog a filter with it. And if you keep that crap, even post filtered a little, in a rain barrel, "stuff" is going to grow in there and render it really nasty. So, you first have to choose how big to make the barrel, so you don't have water sitting around in it for too long no matter what (or handle this some other way, but clogging filters isn't practical long term, nor is keeping it out of the sun so well algae won't grow).
I'm just one of me, and pretty frugal, so my initial barrel can be pretty small. There's another consideration in the pre-processing, in that having some overflow in every collection cycle is a good thing - my top filter uses overflow to self-wash, and any floating junk also comes out of the small overflow hole in the side of the barrel (about 3/4"). When things are scaled right, as here (tuned after some years experience), the system can be really low-effort maintenance.
The barrel is set up so there's a window screen on the top that keeps big junk out, the pickup is off the bottom so stuff that sinks will not be brought further into the system (you clean it out about once a year, easy to just tip the thing over), and so we start with fairly good stuff. The ratio of collection area x average rain amount to barrel size that gives you this overflow on any decent rain both solves and creates some problems...The coarse filtering becomes almost no maintenance, but there are times when you'd like to get more water during a big rain than one barrel full, so you need a way to see how good the water you have is, and can't always just wait a day for things to settle (if they will, pollen doesn't - it ferments...).
So, what is actually the last step I did was to make it so I didn't have to go look at this - it's in a building a little uphill from the one I live in so I can use gravity feed, but when you really want to check it, it's raining or cold and not fun to go out and look. So....raspberry pi to the rescue:
At the moment, the barrel is full, and so is my cistern which IS in a crawl space away from the sun. Showers and clothes washing day! But the intake system first, I'll get to all the other details. Not shown in this picture is a little medium mesh filter on the takeout line that's easy to clean. Needs cleaned every few months, shaded from the sun, and kinda protected or removed in deep-freezing conditions, though I've had them live over a year without dealing with that one.
Here's an amazon link (not a recommendation) to one about like what I used. Small size is good when it comes to freezing and breaking.
https://www.amazon.com/SHURflow-MARINE- ... ef=sr_1_73
Whatever you get, get a spare...that's a rule in all off grid living.
I keep saying things like the sentence above because some people have looked at my plans for various things and without really thinking things through, made "obvious to them" substitutions/improvements that then failed, and then handed me crap about it. So, this is "at your own risk" and if you want to scale it, there might be unexpected things you run into. It's why I'm using so many words to describe what is after all, a conceptually trivial and block-diagram-simple system. It's not simple in reality if you want to live on it rather than just fool around.
You can see the screen over the top which has caught some stuff. What you can't see without a movie (coming later after I do some editing) is all the junk that the high flow just washed off the top - this is pretty self-cleaning, a real boon. If you look carefully, you can see junk on the bottom of the barrel too - mostly little rocks from the shingles. OK, this is fine at some times of day, but what about others, or nighttime? I built a little submersible light with some high brightness LED chips out of a home LED light bulb that had a failed power supply and a piece of glass tubing, a few resistors, and some hot glue. The pi can blink this light source, which sits at at the bottom of the barrel, in the field of view, and shows me the turbidity of the water. Not that easy to automate, but a human can judge instantly. Commercial turbidity sensors, at least those you can afford, start at "way too nasty" and go up from there...this shows you how many feet you can see through the water, not how many millimeters, and doesn't need flow to self-clean, or at least not so far.
I'll be back, this is just a start. I'm going to try to have full plans, even the computer code and schematics in this thread. But this took years to fully work out, and it's going to take days to gather all that, so be patient. If you're in the 3rd world (no judgement call here, where I am might as well be about some things), maybe this will really help you. Just a little bit of inexpensive tech and some savvy can make the truly oldest profession - survival - a lot easier.