Diverters and Pre-Filters for Roof Rainwater Catchment, by Dim Tim

I have had this idea floating around in the back of my mind for some time now, and with all the posts on the subject here lately, I decided it was time to share it with everyone. I hope some of you find it useful.

What got me started to thinking about this was a movie on DVD that I watched recently, titled Twenty Years After. (2008) It is about people that have survived a nuke war, the disease and death that follow, and the hope that humanity will still survive. It is not the best post-SHTF movie that you can watch, but as I watched it, I had little flashes of insight to some aspects of survival and preparedness that I thought would be useful, and this is one of the ones that I want to share today.

In the movie, a mother, and her very pregnant daughter, have claimed a house for their place, only to find that the owner has returned to claim some of his things. He makes his presence known to them by pouring a bit of water down a downspout that they have rigged up to send the rainwater to their living space in the basement, where they collect it and store jars of water on some large shelves.

This got me started thinking about the subject of rainwater catchment, and I have a good number of files on the subject, so I did some extra reading on the subject. There is a lot of information out there on it, and all the commercial products that go with it, but what do you do when you have ZIP to start with ?
Start at the beginning.

So, the rain falls on the roof of a building, it runs down the roof to the gutters, then down the downspout to be flushed away from the building. And now you decide to catch the runoff, and put a barrel at the end of the downspout to catch the extra water. So far so good. But what about the bird poop, asphalt chemicals, etc, that are going to be in the water, not to mention all the other germs and nasty pathogens that occur naturally ?

This is where the diverters come onto play, you divert the first couple minutes of the rain water, to get rid of the grit, dirt,etc, and then divert it back to catch the rest. I see this as a waste of water that could be used to keep you and your family alive a bit longer.
You will most likely be filtering the water to drink anyway, so the dirt and germs are going to be dealt with in the filtering process. The filter will only be able to deal with so much in the way of contaminates, so there are a lot of folks who agree that a pre-filter is a good idea to extend the life of the main filter itself, and here is where my idea came from. I know that there are commercial pre- filters that may be a whole lot cheaper to buy from the point of view on the cost of this subject, but this is about constructing your own from found, scavenged, and recycled materials in a SHTF type situation.

The list of materials that you will need is as follows :

A large stockpot.

Cheesecloth or fine mesh nylon or brass window screening.

A dozen bags of kids marbles or flat marbles used for decoration.

A couple shovels full of builders sand. ( Children’s sandbox sand is a different type of sand, and has some questionable chemicals in it, so do not use this type of sand. Builders sand is just that, SAND. so be sure to use only this type for your pre-filter )

And a good supply of charcoal.

Tools that you will need are:

  • A drill, and a good assortment of drill bits.
  • Center punch.
  • Heavy machinists hammer or a small, one-pound or two-pound sledgehammer.
  • A piece of 2×4 scrap lumber, about two feet in length.
  • A good pair of safety glasses [with side guards]. This is the most important piece of equipment you should have when you build this, because your eyesight is very important to your survival. Wear them!
  • Four bricks, or 2×4 blocks.
  • A large funnel.

To start, place the stockpot on the bricks or 2×4’s like you were going to build a fire under the stockpot for cooking or heating water.
Then, take the two foot 2×4, and your hammer, and place one end of the 2×4 into the center of the inside of the stockpot and give a couple of good sharp blows to the top of the 2×4 to make a depression in the center of the pot to allow for complete drainage of the filter. A slight depression of the base is better than a flat bottom, because it will allow the water to drain at the lowest point and not to run all over the bottom and drop off the edges instead,

Now, take the stockpot, and turn it over so that the outside bottom is now face up. Take your box of drill bits, your center punch, and your drill, and use the center punch and your hammer, to make a punch in the approximate center of the stockpot. Now take and punch six or seven more around the center, remembering to space them about an inch and a half apart from each other. These will be drilled out with a half inch drill bit to form the drain for the filter, and the whole thing needs to have an area of holes about the size of one of the downspouts. This will allow for good and proper drainage of the filter. Once all the holes have been drilled, take a larger bit, and use it to ream out the holes, so that there are not any sharp edges or metal shavings to cut your fingers, etc, and the screen material.

Once you have this done, take the stockpot, and turn it right side up again. Now take the cheesecloth or screen, and mold and form it to fit in the bottom of the pot, and going up the sides, and over the top, to form a sort of inner bucket of screen.
Now you are ready to fill the filter with the filtering medium.

Start by grinding up the charcoal to make charcoal powder. !00% pure charcoal should be used only. If you lay in a supply of bagged charcoal, then you will have to determine how much that you will need for further replenishment of the filter, as well as the other materials needed to make it, so that you will be able to replace or repair any of the components as time goes on. If you don’t have a good supply of charcoal laid aside, you can always make your own using these sites to help you.

Place about 3-to-4 inches of the charcoal in the pot, tamp it down firmly and evenly as you go. Then once you have that done, form another set of screen material like the first one for the charcoal, and place it in the pot on top of the charcoal filter medium. Fill the pot with 3-4 inches of the sand, just like you did with the charcoal, tamp and level as you go. Now, make one more screen set to go on top of the sand, and place it in the pot.

Now you are ready to add the marbles. Same thing as with the charcoal and sand. Place enough in the pot, to get about 3-4 inches of marbles on the top if the filter mediums.The marbles break up the churning action of the water as it hits the system, and the sand and charcoal act as the filtering agents. By separating all the component mediums with the three screen elements, you are able to lift the materials out separate from each other for refill and repair as needed.

Now that you have the filter completed, you are ready to install it into your system. You can install it at the front of the system, where the downspout pours into the marbles, and the drain fills into your storage barrel, or the barrel drains into the filter, before you send it to the main purification filter. Either way will work fine, and if you want to, you can make two of these and do both. It is your choice on this one.
When you set the filter into place for either one, you can take the large funnel, and set it under the pot to catch and direct the water draining off the filter, so that you catch every drop.

After you have filtered the water through this pre-filter, you can then send it on to the main filter, and know that the main filter will not have to try to strain out the extra dirt and germs that would come without doing this pre- filter first. A good one like the Berkey filters will last a lot longer before you have to replace their filter elements, just by making and using one of these. The most important part to remember about this filter construction, is to use as fine a screen material as you can find. Double or even triple up your cheesecloth or screen if you have to, or even use a combination of both if you want. It is up to you, but you need as fine a screen as you can get.

Here are a couple of sites that I found for material source reference. These are not set in stone type of suggestions, they are for visual aid only, to give you an idea of what to look for. Marbles can be found in all sorts of places, and the same goes for the pots. Stainless steel would be the best choice. The ones to stay away from are the ones with the non-stick surfaces.

A source for marbles:

Glass Gems & Marbles from Wholesalers USA

A source for stockpots:

Stainless Steel Stock Pots @ Yahoo! Shopping

When you use the pre-filter, remember to change the sand and charcoal in the system from time to time.
A recharge every 1-to-3 months should keep everything working fine, and you should be able to make the thing work and last for a very long time to come. Hope that this helps some of you out there doing the rainwater catchment thing to add to your survival and preparedness plans. Watch for a couple of other posts that I will send later, on some other thoughts that I had for some other items that will come in handy after a SHTF event.

Be Prepared! – Dim Tim