Tuesday, April 30, 2019

Rain Capture Water Tanks

Here's a question that anybody interested in preparing for future SHTF-style emergencies ought to be asking themselves.  What good is a robust stash of long shelf life emergency food, an arsenal of weapons with thousands of rounds of ammo and a secured location if there isn't a guaranteed water supply?  What happens if the public water system becomes contaminated or simply stops working?

Got a well?  Great!  But how good is that well going to work if the electricity suddenly goes off?  No problem you say, you have a generator or perhaps solar.  Awesome!  But how long will they remain operational?

Got a year round creek or lake in close proximity, or maybe a gravity fed spring straight into your house?  Good for you -- it doesn't get much better than that, and this post probably isn't for you.  But I hope you read it anyway!

For those of us contemplating emergency preparation and not having the luxury of living within close proximity to a naturally occurring source of potable water, it might be worthwhile to put some thought into how we are going to secure a substantial, reliable, potable and replenishable store of water.

The bright idea that I came up with to solve this dilemma is what I call a "rain capture water tank" -- a BIG one.

Below is a picture of the first rain capture water tank that I built in my backyard mini-farm at my previous address -- not the best photo, and the tank is still in the process of being completed at this point, but it is the only photo I can find unfortunately.  I ended up painting it.  And after the first year of service I sunk 4x4 posts into the soil around the tank and cemented them in place, firmly bracing the walls against the enormous outward pressure exerted by the weight of the water held in the tank.

Rain capture water tank, 2000 gallons, next to chicken coup in backyard mini-farm
Features of this water tank:

1) The inside tank liner is 4 feet by 15 feet by 4 1/2 feet in height.  The bottom foot and a half is beneath the soil surface -- I dug the base into hard clay to give the bottom of the tank solid support, knowing that the weight of the water pushing down and outward would be too much for the rather flimsy wood frame and sidewalls to handle without that support.

2) The sheet metal roof extends roughly six inches past the tank on all four sides.  This is to protect the tank from rain of course, but just as importantly the extra roof surface area captures more water than if the roof surface area were to exactly match the tank.  For every inch of rainfall received, my tank will get an inch-plus of rain water runoff.  With the 4' x 15' dimensions of that tank, based on 7.48 gallons per cubic foot, the tank gets 448.8 gallons for every 12 inches of rain water captured.  Divide that by 12, and according to my calculator the tank collects 37.4 gallons per inch of rain capture.  Not too bad.  Due to the fact that my geographical area receives on average 48 inches of rainfall per year, I could count on that water tank filling up every winter.  As it turned out in practice, due to the extended roof surface area, it actually filled up every year by mid-January at latest and I had to disconnect the downspout to prevent overflowing.

3) The tank has a sealed cover made of plywood that is attached to 2x4s fastened across the top of the tank to prevent sagging.  The cover, or "lid" as I call it, is very important for the following two reasons:

  • Prevents dirt, debris and bugs from getting into the water (especially mosquitoes)
  • By preventing light from getting in, mold is unable to form, the water remains pure and crystal clear like a spring-fed underground cistern.  If even a single small shaft of light were to shine on the water for a few days it would quickly mold up, and we don't want that.

4) It has a hand pump installed on top of the cover, reinforced at the base with 2x4's, that pumps water at the rate of one quart per full pump.  The pump output has a garden hose attachment which enables pumping water to all areas of the backyard via the hose.  I never found time to hook up a drip irrigation system to it.

If you're capturing rain water to irrigate the garden or to serve as a backup potable water supply, you're probably going to want a hand operated water pump.  Hose attachments can be added to this pump for minimal additional cost -- hook your irrigation system up to the output and use the pump to water your garden.  Much better than having to carry water from your tank to where the plants are growing.  A duel hose output fitting with on/off switch for each output can be attached -- use one output for watering the garden and the other output for pumping water into the house or other area.

Example of hand operated water pump for watering the garden and pumping water to where you need it -- $160.90
5) The frame of the tank is actually rather flimsy.  Built of 2x4 douglas fir and 3/8 inch cedar plywood inner walls, this frame was only intended to provide the scaffolding and encasement for the custom tank liner.  At first I assumed that with almost two feet underground, the top two feet of water would not exert enough outward pressure to stress the frame -- I thought it would hold rigidly.  I thought wrong.  I got bulging around the top of the tank, and the 2x4 side supports definitely came under too much pressure.  So I kept it only half full for the first year, then the second year I added perimeter supports of 4x4 posts cut to size, four on each side and two on both ends (not shown in photograph as I hadn't completed that work yet), and sunk directly into the clay next to the tank with rebar and concrete to make it as solid as possible against the water pressure.  The concrete-sunk posts did the trick -- no more bulging or stress on the frame.

6) The liner is a custom-made potable water vinyl liner made by American Brand Products, Inc.  I ordered the liner to my specifications, received a quote, paid for it and the liner was shipped to my front door.  If you are thinking about getting a custom tank liner, these guys do it very well.  I never had any issues with my liner for this tank, or with the liner for my newest water tank.  Here's the link: http://www.websweeper.com/liner/tank-liner/

My first water tank worked extremely well, as good or better than envisioned when I had the "bright idea" to build it.  During the five years that the tank was in service, I had the comfort of knowing that should SHTF, I had my water source one hundred percent secured.

Then I decided to move out to a rural location.  I immediately set out to build ANOTHER custom water tank.  Only this time, I went BIG -- 10,000 gallons!!

Rain capture water tank, 10000 gallons
Another view
Above are two pictures of my new 10K gallon rain capture water tank, put into service October of last year.  Working off the success of my first water tank, I did it basically the same way.  Except this time I hired an excavator to come out and dig the hole.

This new tank is 4 1/2 feet tall, same as the first one, but is 20 feet by 15 feet in dimension -- 5 times larger than my first tank.  It has all the same features as the first one -- minus the hand pump -- with a couple of extras.

First, it is located at the highest point of my sloping property.  It is about a 40-foot drop to my ten thousand square foot grow area, so instead of pumping the water I can let gravity do the work for me.  At the bottom of that 40-foot drop I get a really strong stream of water coming out of the 1-inch PVC that I ran from the tank to the grow area.  Plenty of pressure for the drip line irrigation system that I'm currently in the process of putting the finishing touches on.  Hopefully not too much pressure.  I buried the 1-inch PVC pipe a few inches under ground (fair amount of digging), except for where it passes through the chicken yard.  At the midpoint of that approximate 200-foot PVC pipe run, close to my house, I installed a 2-way garden hose adapter with open/close valves.  This way, from that midpoint next to my house, I can turn the water off or on to the garden area without having to walk down to it, and if desired I can route the gravity flow into my house.

Ten thousand foot grow area surrounded by deer fence that the rain capture water tank services
Second, the frame for this monster water tank is not built of 2x4's.  Rather, it is built out of 4x4 treated redwood.  The walls are not plywood, but 3/4 inch particle board -- extremely tough stuff.  The 4x4s are attached with metal bindings and 4-inch screws.  Where the 4x4s meet at the corners I used 7-inch long, 1/2 inch thick hex-head "bolt screws" to ratchet them tightly together.

Third, I installed an overflow outlet pipe on this tank so that I wouldn't have to worry about the water level rising past the liner.  The overflow works great -- last rain we had a week ago, I went out to the tank and observed the overflow water gently trickling through the overflow pipe and into the crushed rock retainer wall, where it seeps down to the ground and then down the hill right along with all the rest of the rain water.

Finally, the lid (or cover) is heavy duty -- I can walk on it.  Supporting the eight 4-foot x 8-foot sheets of plywood that form that cover are two rows of cedar 2x4 "T-supports".  Each T-support is set on a flat 8-inch square paver with rounded corners, which itself rests on a half-inch bed of fine sand.  This way the pressure of the weight on the cover will not damage or otherwise impact the bottom of the tank liner.  I bolted 16-foot 2x4s to the T-supports just under the cover for additional support.  The 4x8 foot plywood sheets that form the cover are attached to not only the T-supports but to the 16-foot 2x4 cross-supports also.  It is very firm and solid.

There were about six to eight inches of free space on all sides of the frame once I got it completed because I asked the excavator to carve out a little extra working room when he dug the hole.  After I finished constructing the frame, I used my tractor to pour and pack crushed rock into that free space, then mounded up a couple of additional loads of crushed rock retainer around the front and sides where, due to the slope, more of the tank was above ground.  Due to the "bulging" issues I had with my first 2000-gallon water tank, I went full-retard on making sure this tank had all the side support required to prevent any outward pressure from putting undue stress on the frame.  It is currently topped off and no bulging.  But I'll continue to keep a close eye on it, ready to pack more crushed rock around the sides if needed.

But that's not the end of this long-winded story.  I felt like I needed even MORE water.  I came across a local company that had a special deal going on 5000-gallon prefab vinyl potable water tanks.  I picked one up for $2000 including delivery.  I put it on top of the crushed rock pad where the previous owners had installed a mobile horse stall.  Then I rerouted the west-facing side of my barn roof's rain runoff through the downspout, into a 3-inch pipe which I attached to a tension wire for support, and ran that to the top water tank input.  You can see it in the pic below.

Rain capture water tank, 5000 gallons, with 3-inch pipe routing water from barn downspout
Another view
Due to the large surface area of the west-facing side of my barn roof and the large amount of runoff it captures, it took less than two months for the 5000-gallon water tank to fill up.

At the bottom of the tank is the output spout which I opted to have installed with a garden hose adapter.  I don't get much gravity feed pressure in my grow area from this tank due to it being only ten feet higher in elevation, at most.  I'm going to use this tank to water my small hazelnut orchard this summer, and as time goes on and circumstances allow, I'm probably going to plant some cherry, peach and pear trees next to the hazelnut trees.  I'll have plenty of water in that 5K tank to keep them all well-watered.  Maybe even put some goats down there, who knows what else.  I have enough water to handle it all!

Garden hose attachment at base of 5000 gallon rain capture water tank
One final critical piece of equipment I thought I would mention is this hand pump shown below.  I took it to the nearest Home Depot where I found the correct fittings to adapt the intake and output of the pump to standard garden hose male and female fittings.  I mounted it on 3/4 inch particle board.  When I'm ready to start pushing water through my new irrigation system-in-development, I'll go to the midpoint 2-way hose adapter, hook my pump up to the free outlet and start pumping.  I did it for the first time last week and it took about five minutes of pumping to get the water flowing to that midway point.  Once there, it already had significant pressure.  I closed the valve on that outlet, opened the valve to the garden irrigation PVC line, then hauled ass down the hill to watch the water come out.  It was a thrill to see how powerful the jet stream was.  Gravity can work FOR you sometimes.

Hand pump used to pull water from rain capture water tank into main line and start gravity feed
In closing, an opinion.  No matter what steps you are taking to prepare for an uncertain future, guaranteeing an adequate water source should be a key consideration.  I only bring this up because I've talked to several people about their SHTF plans who seem to have overlooked the possibility that public water systems might stop working in an extended emergency situation.  If that happens, a case or two of bottled water is not going to be enough.  Not even close.  Everybody needs water -- LOTS of water.

Here's the bottom line: A substantial guaranteed source of water is still no guarantee against all future unknown threats, but if we don't plan and take action now then we're damn sure guaranteed to be unprepared when everything goes to hell.

Thanks for reading.


  1. I like it. Plenty of water no doubt. I have roughly 2500 gallons in various tanks and barrels. Also built a 12v powered water purification system on a hand truck so it can be moved to any source of water. It uses a Rio 2000 ceramic candlestick for a final filter element after passing through a sediment and carbon filter. The on board pump is a Jabsco smart pump...low current ...high PSI and volume.

    1. Hi Farmer. It looks like you've put a lot of thought and effort into making sure you have your water situation taken care of. I take it you have some streams or ponds around your place that you contemplate maybe needing to take water from at some point, based on the cool water filter setup you describe. That's one of the drawbacks of this property -- no natural water source, though there are ponds and large year round creeks on surrounding properties. That's why I thought I better get my butt in gear and get those 10K and 5K water tanks in service. Glad I got it done, now on to the next big project! Thanks for posting!