Could rainwater catchment systems become the answer to Panama’s water supply inadequacy?
Water quality and water availability are becoming a big concern for land developers and home owners in Panama. This year’s El Nino effects on panama’s water reserves have forced consumers to look closely and more carefully to alternative water supplies.
Even though a rainwater catchment system by itself is not a viable potable water source, when coupled with a filtration system, it could become a stand-alone household water supply system.
What are the considerations prior to building a rain water catchment system?
Before you take a trip to the hardware store, there are a few minor calculations you will need to consider for your particular residence. 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.
Roof Water Collection Capacity
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.
The calculation then is 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.
For the Boquete, Panama area, a 1000 square foot roof would be able to yield:
- Assuming annual rainfall is 130 inches/yr (or 10.8 feet)
- Assuming 98 % efficiency for collection (typical for tin roofs)
- 7.5 gal./cubic ft.
Then:
- 10.8 ft of rain/yr * 1000 sq ft * .99 = 10,725 cubic ft.
- 10,725 cubic ft * 7.5 gal./cubic ft = 80,437 gallons of water collected per year (or 220 gallons a day).
Tank Capacity Calculations
Assumptions:
- The average daily household usage is 40 gallons per person per day
Then:
household use in gal./day *number of persons * possible number of days with no rain = X gal. of storage needed
Materials
No meaningful recommendation can be given (especially in Panama) on the type, amount and cost of materials because this is a matter completely depended on the geometry and special characteristics of your system. Theoretically any capable professional (and that’s a big statement in Panama) would be able to quote you with the materials you’ll need and their prices. At the end, use common sense. If it does not make sense to you then it’s probably not good.
Setting Up Your System
The following are some basic considerations and points to consider before and while you setting up our rain catchment system:
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 can be compacted. Sprinkle with 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.
*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 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.
Filtration System
If you are going to be using your rainwater catchment system as your potable water source, then you need to set-up a water filtration system as well prior to introducing your water to the house supply. There are a number of efficient and cost effective filters available in Panama. Check with your local hardware store for options.
Here is link to the basic water quality and water filtration considerations.
Do you still need more info? Check out the link bellow:
Rainwater Catchment Systems for Domestic Supply: Design, Construction and Implementation
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