Thanks for what SurvivalBlog done for the prepper community. I just had a feeling weighing on my heart to share this information. So here it is.
In any survival situation, water is in the top two things that must be had in order to survive if not at the top of the list. What I'm going to describe is how to set up a rainwater catchment system. The first thing to do is decide how much water you want to harvest. Then you need to decide how to hold that amount. Whether it is a couple food grade 55 gallon drums linked together or an underground AquaBox system that can hold thousands of gallons. Next you need to set up your structure, be it your home, shop building, barn, or animal housing, you will need to have guttering with a down spout. A steel roof is preferred by most for this, but any roof will work. At this point you need to know how you are going to use the water that is collected. If you are just going to use it to water your garden or your livestock, it doesn't need to be filtered. If you are planning on using it for drinking water, then it will need to be filtered or purified in some fashion. This essay will go through the steps for drinking water.
For every square foot of roof that you can harvest, you will get a half gallon of rainwater for every inch of rain. [JWR Adds: To be precise, multiply .623 gallons by the number of square feet of your roof.]
Read more at eHow: How to Calculate Rainfall for Harvesting
So you can figure how big of tank you need by multiplying the square feet by the average rainfall for your location and that will give you an rough figure of how much water you can expect from that roof.
Let's start at the top of the water system. You have your roof with its guttering attached. Does it have a leaf guard mounted on it to filter out the leaf litter? If not you can install a Invisaflow Flex Gate Downspout Filter on the downspout and install a stainless steel mosquito screen on the bottom where it connects to a First Flush Diverter to keep the little suckers out of the tank. They will find their way into your tank otherwise. In some locations, these are required by code.
After the water passes through the Downspout Filter, you will want to install what a First Flush Diverter. There are several styles of these, but the basic design is this. The water comes into the Diverter and fills it up, doing so causes a rubber ball to float up to a tee connection. The first water off the roof is in the bottom of the Diverter with all the bird droppings, dirt and small bits that the Basket Filter missed. Once the ball goes up to the tee connection, the rain water is diverted to a second pipe and sent on its way to the tank of your choice.
Now for the tank. Is it light or dark in color? If sunlight can penetrate, it will grow beautiful green algae. Now, unless you like the taste of algae in your ice water, you will want to paint your tank a dark, opaque color. The actual color does not matter as long as light cannot get to the water. After the tank is painted, you will need to attach the pipe from the Diverter. Use a hole saw the same size as your pipe, you want as tight a fit as possible. After inserting the pipe, seal all around it with a silicone caulking. Next you will want to put in an overflow pipe of the same size as your inlet pipe. Place it as high on the side of the tank as possible for the maximum amount of water harvest. This pipe will also need a mosquito screen as well. Attach as above. Lastly on the tank you will need to attach your water line. Depending on location and use will determine the size of line or lines that you want.
Running your water line from tank to destination, you have a choice of running it above ground or trenching it in. In some locations you may have to run it under the frost line to prevent freezing and to meet code requirements.
The following is one scenario that could be used for hilly terrain in an off grid situation:
Up-slope from your cabin you have a small barn/wood shed/chicken coop and you decide that you want a gravity fed water system that could also be used for fighting fires if the need arises. First thing you do is attach the correct length of guttering to the lower eave of the building. You lucked out in the fact that it already has a steel roof. After installing the leaf guard and down spout, you attach a Basket Filter that you picked up at a local home improvement superstore. You then install a First Flush Diverter you built from plans you found on YouTube. You run the diverter line to the 275 gallon poly tank that you picked up at the farm and ranch store. (You painted it the same color as the barn/wood shed/ chicken coop.) You then dug a trench from the tank to the cabin and ran a 2 inch water line to within 75 feet of the cabin. Here you plan on installing a freeze proof faucet for fire fighting. You then ran a 3/4 inch line that you attached to the 2 inch line the rest of the way to the cabin. Once at the cabin, you run the line inside to a small holding tank with a spigot or to an in line filter then to the holding tank. After back filling the trench, you run the overflow pipe in another direction. You just happen to have some 4 inch flex landscaping pipe and run the overflow pipe into it and run it towards your pond. After trenching and back filling the overflow, you stack up firewood around your tank to better hide it from those you wish not to know about it and to protect it somewhat from possible gun fire from same. Not to mention it will keep more sunlight off of it and partially insulate it from winter temps. Another option is to bury the whole tank which will protect it from freezing, gunfire and sunlight.
Ideally, you would have some form of rain water harvest on every structure at your retreat. It can be used to water gardens and orchards, water all livestock, top off your fish pond with the overflow from the tanks, keep your hydroponic set up with fresh water, run a line to that outdoor shower house with the solar heated water system on the roof. You could run it to the automatic water system in the rabbit house or chicken coop.
Another type of rainwater catchment would to use a pond. You could use an existing pond but it would require draining in order to install the pipe line. The best bet would be to install the piping during construction. Before the dam is complete, take a 4 inch PVC pipe and run the non-flared end through a hole in the bottom of a 5 gallon bucket that you cut with a hole saw. You did drill countless 1/4 inch holes all over the bucket first didn't you? I thought so. Now replace the bucket's lid that also is quite holey. If you haven't removed the metal handle to the bucket, now would be a good time. This will be your filter to keep your fish stock from being sucked down the pipe. Now install the 4 inch PVC pipe, several feet up from the the bottom of the pond, through the dam. You want it up, off the bottom for two reasons. First, you want it up out of the muck that is on the bottom of all ponds. And second and most importantly, you don't want to drain the pond if someone accidentally or purposefully leaves the line open.
After the pipe is installed and the dam finished, you will want to install a down sizer. Either a 4 inch to 3 inch or a 4 inch to 2 inch. Right behind the sizer, you need to install a valve so the line can be turned off at the source. Now is when you run the water line to you choice of location. End the line with a freeze-proof faucet. A pond with fish in it makes a great source of water for a garden or orchard. The fish fertilizer is loved by all vegetation. This set up will also give you the head needed for some firefighting applications also, depending on location of pond to fire. You could even plumb this into a drip irrigation system or soaker hose network. Just downsize the line from 2 inch to 1 inch or smaller so that you don't flood the area too quickly.
Now these are not the only rainwater catchment methods out there, they are only two methods. I'm sure that there are several SurvivalBlog readers that know other ways and hope that they share them. Also any critiques or advice is welcomed.