Monday, August 6, 2012

Designing And Installing A Rain Water Catchment System

We are just finishing up on a rainwater catchment system on our house
and our first big decision was what kind of tanks to use.

Of course we would have loved to have had nice galvanized tanks, 
but the reality is that the above ground polyethylene tanks we chose were more affordable, 
are easier to handle and install, are able to be moved,
 and will last much longer than the metal.

Many people go with below ground tanks but that requires different tanks,
 and the added cost of digging not to mention the disruption to the landscape,
and the added factor of pumping the water back up to the point of use.

We leveled off pads for the tanks
 and because our soil is so fine it made a suitable rock free base.

Otherwise 2" to 4" of sand would be best to prevent sharp rocks 
or anything else that might puncture the polyethylene.

The above 1650 gallon tank comes with a covered hole on the top 
with an optional screened basket
 that fits in securely to help filter out debris for the water intake 
(where you see the downspouts entering).

The black 2" ABS pipe is the overflow which we installed,
 but we opted to have the supplier drill the hole and install the fittings for that 
and the 3/4" valve on the bottom right for hooking up the hose to.

Installing the fittings is not particularly hard but our supplier had it down
and it was well worth having him do it after the tanks are placed
and we could see where we wanted things to go.

By the way, the 1650 gallon tank is the most gallons of storage for the money;
each supplier is a bit different
 but it seems that 1500+/- gallons is the so called "sweet spot".

As part of this project we also installed the gutters on the house
using 10' sections of galvanized metal gutter from a local hardware store.

There may be people who specialize in gutter installation in your area
 but we chose to do it ourselves because most installers use a painted aluminum 
and we wanted the galvanized,
and also we have much experience with the process.

Installers also often times use flimsy attaching brackets.

In high snow areas be sure you design your gutters to withstand heavy snow.

For more on installing gutters check out the last part of my post:

Above shows the gutters and the overflow outlet.

PVC can be used for the overflow but I much prefer working with ABS pipe 
as it is more flexible and the glue is not as toxic;
and I hope the black color will prevent potential freezing up on winter days.

Unlike PVC or the polyethylene tanks, ABS is not rated for potable water use.

For this tank I left the overflow pipe higher to collect water in 5 gallon buckets.

More stone and gravel will be added later to prevent erosion from the overflow.

The orange metal fence post holds the overflow pipe in place.

Above is a 550 gallon tank.

Each downspout was rated for how much roof area it covered,
 letting us figure the yearly amount of rain we would get.

We sized the tanks to roughly collect 25% of the yearly total at each downspout,
a number I pulled from the hat as I could not find a recommendation
 as to how much rain water to collect.

Each person will have a different need 
and I would suppose your yearly rainfall amount,
 what times of year you get your rain, 
and whether you are using the water for landscaping or domestic use
 will factor in to your decision.

To convert square footage of your roof to gallons of water use the following:
sq. footage x .62 = gallons of water from 1" of rain.

Multiple that by your yearly average for precipitation,
in our case 10"+/- per year (at 6200' in northern New Mexico) is a conservative estimate.

Surprisingly in searching the internet I found different conversions 
but .62 seemed the most used.

We tried to place the overflow and the water valve
 where they would catch the most sun in the winter (above),
and we are attempting to ditch the overflow away from the house 
and to planted areas, particularly trees.

More stone will be added above to prevent erosion underneath the tank.

In choosing and locating the tanks consider the height of the downspout,
 the height of the tank, 
and the amount of drop you need to get from the downspout to the tank.

Of course always consider where you want the water,
and how you will get it there.

I prefer to keep the tanks as far away from the house as possible,
as you never want overflow water next to the house.

We have 3 green tanks and this one brown one.

Above gives a good view of the faucet valve.

The connection to the tank is a polyethylene fitting,
which goes to a 3/4" galvanized nipple, a 3/4" PVC valve,
another nipple and finally the brass hose adopter.

This overflow is a tee to direct the water both directions.

Our supplier for the tanks was Charlee Myers
in Tres Piedras, New Mexico
and we were very pleased with the service and expertise that Charlee provided;
check out his web site.

He also delivered the tanks, set them up,
 and installed the fittings for the valve and overflow.

Now if the historic drought we are in would just let it rain.

To see more on this topic after a year and a half of use go to the post:


  1. I would like to know what you are doing with the water. Are you using it for your home water supply, if so, how are you getting into your house? Are you drinking it? If so, what kind of filters. Or are you just using this to water a garden?
    I live in a tiny house with no water supply. I have one rain barrel and would like to get a large tank like this to set up for my house, at least for showers and washing dishes and doing laundry. I am looking for info on how to do this

  2. Hi Roxy, I am sorry to say I have no direct experience with using rain water for domestic use. Our system is for landscaping only, at least at this point. I do know that there are quite a few people out there who do use it for domestic use. Charlee Meyers who we bought our tanks from uses rainwater for most of his domestic use so you can check the link above and contact him and see if he could be of help. My guess is that an under ground tank would work best in freezing climates. Filtering is not a big deal but may require some up front money for carbon filters and infared filters. Again this is not an area that I have any experience. I remember reading an article in Fine Homebuilding Magazine many years ago on the subject but that was a while ago. I would hope that you could find much more in an internet search. Good luck and good for you for having a tiny house.

  3. Roxy, I use rainwater for 8-12 months a year. For maybe ten years now. My wife insists we filter for direct drinking because we buy a tanker occasionally. I have brick domed and cement plastered underground tanks. I pump to an evlevated tank as needed. I need a bigger storage tank.

  4. Ches, I check how people arrive on my blog from stats and then found this blog. And you had linked me! Great, Thanks. So I put a link to yours on mine.

    Good blog, thanks for making it. Will read more.