Please remember that this system is not
adequate for drinking water uses.How to Build Your Own Rainwater Catchment System
- A Simple Cost Efficient Approach -
"In the next two decades water use is expected to triple in the world, corresponding to increases in population, erosion, runoff, dewatering, and salinization"
from the book Grand Challenges In Environmental Science
Having your own rainwater catchment is just a weekend of work away. The extra water your residence collects can be used to water the garden, wash the car, or be saved for when you need extra water during a drought. There are countless ways you could use the collected water, especially if you install a water pump that can supply water to the house. You can learn more about this from the website (Kyle's website).
Please remember that this system is not
adequate for drinking water uses.
* Getting Started with some Preliminary Questions
*Time To Buy Materials - What will I need to buy and how much will it cost me?
*Time To Set Up My System: what considerations are important to my system's set up?
*Do you have questions? Links to email
Getting Started with some Preliminary Questions:
Before you take a trip to the hardware store, there are a few minor calculations you will need to consider for your particular residence. The type of material your roof is made from, how much rain your roof will collect, and how big your collection take should be along with daily water use and annual rainfall are all important questions that need to be addressed before getting your project started.
1) What type of material is my roof made from?
A metal roof is the number one choice for collecting rain water, but almost any material is fine.
except .... for roofs made from tar and gravel or asbestos. These
materials will leave
unwanted chemicals in the collected water.
2) How much rain will my roof collect?
Measure the perimeter of your roof then calculate the area as if the roof were a flat surface (like a floor
plan) - no need to take pitch and slope into account because using the perimeter to calculate the area
will yield an answer that gives you the surface area the rain falls upon. Please see the figure below for
clarification.
Example For Humboldt County:
1) annual rainfall is 42 inches/yr (or 3.5 ft)
2) Lets say the perimeter of the roof is 20 X 50 = 1000 sq. ft.
3) assume 80 % efficiency for collection (typical for shingled roofs)
4) 7.5 gal./cubic ft.
3.5 ft of rain/yr * 1000 sq ft * .80 = 2800 cubic ft.
2800 cubic ft * 7.5 gal./cubic ft = 21,000 gallons of water collected per year
*If you do not live in Humboldt County you would calculate the annual catchment as follows:
(roof catchment area/1000 ft) * (550gal.) * (annual rainfall ft.) = amount you could collect. If
you are wondering where the 1000 and 550 are coming form - they numbers come from the
conversion factor for a 1000 sq. ft. roof, which yields 550gal./inch of rain.
3) How big should my collection tank be?
Note: a
conserving house hold uses 25 - 40 gallons per person per day.
Example: 4
person household * 30gl/person = 120 gal./day for the whole household.
Now its time to consider how much of a reserve your household needs. Say you live in a very dry area - you might
want to consider how much water your household would need to save to meet the household usage if there was a 75
day drought. If you live in an area that rains rather frequently then you may only need to consider the possibility of a 50
day drought. 120 gal./day * 50 days of drought = 6000 gal. of storage needed
or more generally ....
household use in gal./day * possible number of days with no rain = X gal. of storage needed
This is the collection tank that CCAT uses.
Another criteria that can be used to size your tank is to consider the length of the rainy season. Split the rainy season
into months. Document the monthly rain fall in gallons. Then subtract the household's monthly use of water. The answer
will show the amount of unused rainfall each month. The size of the tank will have to accommodate the month with the
largest excess. If there is excess water from the previous month, it must be added onto the current month's excess like a
running total.
Example
For Humboldt County:
April is the one of the rainiest month on average. Once again lets assume a roof will a collection area of 1000 ft with 80 %
efficiency.
1000 sq. ft. * 1/3 ft rain x .80 = 400 cubic ft
400 cubic ft * 7.5gal./ cubic ft = 2000 gallons of rainwater
lets assume the house uses - 1725 gallons used
275 gallons excess
The excess is calculated as a running total from month to month. Before April, there was a total accumulative excess of
6150 gals. 6150 + 275 = 6425 gals. After April, the monthly rainfall decreases significantly, which leaves April with the
largest accumulative excess. The tank must be able to hold about 6450 gallons of water. Remember, if you have a circular
collection tank, the volume it will hold is calculated from the equation:
Vol = surface area * height of tank or .... Vol = 3.14 * r2 * height ( r = radius of tank)
4) Recap: criteria to consider before you get started.
* material roof is made from
* size of collection surface (roof)
* size of collection tank
* annual rainfall for your area
* daily household use
Time To Buy Materials - What will I need to buy and how much will it cost me?
Note: I will be listing the cheapest and easiest to install materials -
there are many others
if you want invest more money into your system.
*Barrel / drum : $free - ? ( You can usually find one of these just laying around some where)
Polypropylene: $0.35-$1.00/gal. (These are easy to move while empty, unlike cement tanks)
Metal: $0.40-$0.60/ gal. (THIS TYPE OF TANK CANNOT BE USED FOR
DRINKING
WATER UNLESS A LINER IS PURCHASED)
If you look closely at the top of the dark barrel you can see how the water makes its way from the gutter to these holding tanks (light colored
drum and dark colored barrel) into the PVC piping to the collection tank (picture shown above).
*Gutters: $0.30/ft do it yourself (Many times gutters will come with instructions - make sure to buy
enough bracing to connect the gutter to the house - this part is essential and if not done right it can lead
to major problems.)
NOTE: to keep gutters clean you could install: leaf guards, strainer
baskets, or a funnel.
* Piping to and from the tank: $10/ 10 feet approximately (Diameter of pipe is dependent on the size
of the collection area.) PVC Elbows: $2/ piece (There are two types: pressure fittings which lack a
flange on the end, and fittings for pipes that are not under pressure.) Solvent Cement: $5 -15 (To
use this material the temperature must be above 40 degrees F.)
PVC piping from house (holding tank picture shown above) to collection tank at CCAT
You can get creative with the ascetics of the system.
* Materials for flat and stable surface: AKA Crash Pad: total $60
4 - 2 X 4 of appropriate length to box in your tank's diameter: $10
road base: $20
1 bag of Portland cement: $30
or... The collection tank can be stabilized by digging a hole a few feet deep to insert the tank into place.
Remember that different soil types behave differently so this may not always be a viable option.
NOTE: Please map our your entire system - including all elbows, brackets,
and odds and
ends before your trip to the hardware store. It sure is a drag to go back to the hardware
store for one small item that you forgot.
Time To Set Up My System: what considerations are important to my system's set up?
There are a few pointers given above in parenthesis, but I have a few more before you get started.
1) Inlet to tank should be lower than the down spout to gutter.
2) Shade and camouflage from trees are preferable.
3) Tank should be placed on flat and stable surface. One trick is comparable to a sandbox (AKA crash pad).
Make a small box around the area where the your tank will be placed not more than a few inches in height.
Fill box with road base, which is cheap and compactable. Sprinkle with Portland cement. Rake,
check to make sure surface is level, and dampen with water. Let the contents of the box dry
naturally.
4) Hanging gutters properly can be tricky at first so remember ....
*Measure length of eaves to determine gutter sections
*Downspout is needed every 40 - 50 ft of straight gutter run.
*Count up the number of downspouts - double this number to get the amount of elbows you will
need - this accounts for overhang and the turn from the downspout to the wall.
*Count the number of 90 and 45 degree turns in order to buy the correct shaped elbow in the right
quantity.
*Down pipes come in lengths of 10 ft. - one is need for every downspout - more is needed for a
multilevel house - less if PVC piping goes up the wall to meet down pipe.
*Count number of down pipe connectors needed.
*Count the number of down pipe straps needed.
*Count number of end caps needs.
*Brackets are needed every 30 ft along facia board or one on each rafter end.
*While many gutters come with instructions a universal rule is that gutters should be pitched towards
the downspout 1/4 - 1/2 inches per 10 ft. To do this measure the run of the house, which is the
distance along the roof edge which needs a gutter hung.
Example:
Let's say the run of your house is 40 ft (round to nearest 10 ft increment).
At a
1/4 inch drop per 10 ft. that means you'll need 1 inch of drop total. It is always good to make a
guide before installation.
*Install either leaf guards, strainer baskets, or funnel to help keep the gutters clean. Leaf guards are
placed on top of the gutter, while strainers and funnels are placed were the gutter meets the
downspouts.
5) When install piping from the gutter thorough downspouts to tank the size of the piping is dependent
on the catchment size.
Basic
guidelines: 5000 sq. ft. of collection surface = downspout of 3 inch
diameter pipe for
every 50 ft. of gutter run tied to a 4 inch diameter PVC running to the collection tank.
For
smaller surfaces = downspout of 2 inch diameter pipe for
every 40 ft. of gutter run tied
to a 3 inch diameter PVC running to the collection tank.
6) When connecting PVC piping with PVC solvent- cement give the pipe a quarter turn back and forth
to spread glue around. Beads of glue around the outside ring of PVC means you've done a good
job - and with luck the pipes will not leak. Also do not forget to give yourself leeway when cutting
the pipes. A standard rule of thumb is about 3 inches extra between fittings.
7) When deciding where to place your tank - remember to place it on the highest ground possible.
because...
water gains one pound per square inch of water pressure for every 2.31 feet of rise over lift:
2.31 feet of lift * 40 psi = 92.4 feet.
or more
generally...
2.31 feet of lift * desired water pressure = needed height of tank placement or...
2.31feet of lift * X psi = height of your tank placement
1) Kyle - also doing Rainwater Catchment for CCAT through ENGR 115. There is no available address yet.
2) www.ircsa.org - international organization
1) Ornales, Susan. "Rainwater Catchment System in Humboldt County", 1990's. This small document is
available at CCAT.
2) Banks, Suzy and Heinichen, Richard. Rainwater Collection For The Mechanically Challenged, Tank
Town Publishing, Dripping Springs, Texas, 1997. This book is also available in the reference section
at CCAT.