9/10/12

Rainwater Harvesting in Honduras


FYI: This is a very lengthy post created for those interested in our rainwater catchment system and as a resource for other folks working around the world that may be looking for ideas. Many of the ideas that we used in our system came from outside, undocumented sources (to which I am very thankful ) and some are original ideas. Whatever the case, we hope this information can be to use to those interested in utilizing the amazing resource that God has given us in rain. Please contact us if you have any questions or suggestions, we’d welcome your feedback.
 

A storm rolling into Las Lomitas.

History
I started thinking about harvesting rainwater before we actually came to Honduras. I had done some research into the climate here and realized that there would likely be sufficient rainfall for our personal needs. As we’ve experienced thus far and from investigating with the locals, the climate here has a “dry” season from late February until early May in which a storm only passes once every 2-3 weeks. May experience above average rainfall as a miniature “spring.” From June through October, precipitation becomes very regular, with rainfall starting around 5-6PM and ending around 10PM. Among these regular rainfalls, at least one strong storm passes per week. Then, in November, the “wet” season starts and runs through early January. During this time, the temperature drops and it is common for rain to go days without stopping.

The most precipitation we’ve seen out of a storm, since we began measuring in May, was 6+ inches in 5 hours (the rain gauge maxed out in this time, so who knows how much we actually received.) With a metal roof, it seemed that the apocalypse was upon us.

Since we receive one hour of low-pressure water, three days a week, it seemed insane to not harvest this water in some capacity. Using the system described below, we have water 24/7 in the taps of the house: two sinks, toilet, shower, and outdoor tap.

 

The System

Rain Collection


Our collection system collects water from the aluminum/zinc roof over our house  (including our porch, this is ~600 sq.ft. of floor space).  The water from the roof falls into PVC gutters that in turn empty into 3” drainage pipes that run toward the cistern. Between the roof and the cistern, we have included a plastic barrel that acts as a barrier to capture the first 55 gallon wash from the roof. According to a few studies I’ve read, this should effectively capture 85 percent of the contaminants on the roof. Here’s how the barrel works. 


The first water from the roof falls straight down the pipe past the “Y” and passes into a 2” pipe that passes into the barrel. Once inside the barrel, the 2” pipe passes through a reducer into a 4” pipe, from that 4” pipe, it passes through another reducer into a 6” pipe and out the holes cut into the bottom of that pipe. Within this pipe is a Styrofoam ball. As the water level rises within the barrel, so does the ball. The water continues to pass the ball until the ball arrives at the 2” reducer, at which point the pressure that the barrel exerts on the ball effectively closes off the barrel to additional rainfall. The water that continues to fall can now not pass the ball and begins to back up the tube until it falls through the “Y” and into pipe that continues to the cistern. The dirty water remains sealed in the barrel for later use (accessed through a faucet we installed at the bottom). The important part to remember is to always empty this barrel after each storm. If not emptied, the next first wash will fall directly into the cistern. However, the barrel can be set to “self-drain” by leaving the faucet part open. However, we normally use this water throughout the day for the garden, etc.

Once the water passes the barrel, it passes through the 3” drainage pipe underground and enters the 6000 liter cistern.  The only notable feature in this stage is the outlet into the cistern. The outlet pipe passes to the bottom of the cistern and then angle’s ninety degrees straight up. The pipe is positioned like this so that incoming water flow up and does not disturb any sediment that may have collected on the bottom.
Once the cistern fills, any excess fall into an overflow pipe positioned 2” below the ceiling of the cistern. From there, it runs into the home’s central drainage pipe and off towards the road it goes.

 Water Extraction

 

From the cistern, water is collected through a 1.5” pipe and pumped into a plastic storage tank positioned on the roof above the shed (this a 5’x10’ section of 4” thick reinforced concrete). This water is collected 6” below the surface, since theoretically, this is the cleanest water. The idea is that the dirtiest water is below, since most contaminants settle to the bottom. However, some contaminants also float, so you don’t want to collect the water directly from the surface. So, in order to make this collection pipe float, we made a hole in the end of the pipe and connected a standard plumbing float with a 6” arm. In order to create a joint that allows the pipe to raise and lower with water level, we made an elbow using a double layer of rubber bike inner-tubes stretched over the ends of the pipes with PVC “ribs” in the middle cut and sanded from the same 1.5” tube to prevent inner-tube collapse between the two pipes. The inner-tubes are held in place using brass exhaust clamps (brass to avoid rust). 

The water arrives on the roof using a very simple, hand-operated (no electricity here) deep-well pump that is positioned on the platform with the tank. 30 minutes of pumping fills the 750 liter tank.When the cistern is full, the water travels vertically about 12' and horizontally about 15'.

 Water Distribution

 
From the tank, the water is lowered through a 1” tube to the house’s 0.5” distribution line. If we don’t need the water for the garden, we last ~10 days on one plastic tank of water.  Using the tank to liberally water the garden, it lasts about three days. 

This system has worked alarmingly well. When we “opened” the system in May, the cistern filled in less than 2 hours. We were astounded. We expected weeks! Needless to say, it was an exciting moment when water started flowing in. As a result, the cistern is nearly constantly full to the brim, with all the excess (including floating contaminants)being shuttled 150 feet away to the main road’s drainage ditch. Having running water available in the house has totally changed our lives. No more bucket showers in the shed. No more need to use purified water for teeth brushing. No panic if the community water doesn’t come one day. No more bucket sitting next to the toilet for flushing. 

The water purity is somewhat questionable since there is no actual filtering taking place. However, two weeks after the system was “opened” we had a water text performed, and its result was free of fecal coliforms and several other popular nasties. I occasionally drink the water if I’m feeling impatient, but for the most part we stick with purchased purified water (at one dollar per 5 gallon jub, it’s hard not to).  We plan to add a couple levels of simple gravel and sand filtration over the coming months, but as of now, we’re very happy with what we have. 

The Cistern Construction Process.

By far, the biggest challenge of the project was designing and constructing the cistern. We decided that we wanted to place the cistern below ground in order to save space above ground for the garden. For the same space-saving reason, we decided to place the cistern below the porch.
Using a very comprehensive calculator we found online HERE, we decided to aim for a storage capacity of  6000 liters. As a result, we dug (with pick and shovel) a big, big hole:  10’ long x 5’ wide x 6.5’ deep. It took us about 3 days to dig the hole, and it was pretty delightful work for those that may be wondering.
And fantastic for trapping curious children.
Once the hole was finished, we dug a 6”deep ditch within the hole around the perimeter to make the foundation for the cinder block walls. We filled this ditch with rocks and concrete, with 3/8” rebar pointing up every 2’.



From this point, we layed the 4” blocks, filling in each hole in the block and placing rebar between every two lines horizontally. In order to have enough room to work, it is necessary to leave at least 6” of space outside of each wall.  At every two lines, we also backfilled the space left outside the wall with the dirt we had removed earlier. We also left a hole to pass the three tubes entering the cistern.


Once the block walls were complete, we plastered them with a mix of fine sand and concrete. Once the plaster was dry, we put on a final smooth coat of pure cement paste. 
Once the smooth coat was dry, we poured a 3” thick concrete floor. After a couple days of allowing all of the concrete to cure (always maintaining it wet to cure well). We began the process placing the roof.  We wanted the porch to be one continuous piece of concrete, so in order to accomplish this. We created a rebar cage that sits two inches below the level of the final floor, sitting on the porch and house foundation. Tied into this rebar cage is a metal access hatch we had custom-made for the cistern.

Before the pour and placement of the cage, we created a form for the roof using 2x10 planks cut to the size of the final product.

The side walls were nailed into the concrete with concrete nails and the top planks were supported with 2x4s placed within the cistern. Having cut a hole for the access hatch and placing the rebar cage above it, we were ready to pour.


We poured the porch/ceiling with 2" above and 2" below the rebar. We then left the supports in place for 48 hours to allow all to cure well. We then entered the cistern and began to remove the forms through the tiny access hole. Thank God, all of it fit and was removed fairly trouble free.




We then cleaned the cistern and applied a final double coat of water-proof liner commonly used here for drinking water tanks and pools. After two more days of drying, we were content with our set-up and we opened up the pipes to allow the water to come in. With the setup we have here, we don’t seem to be losing a drop of water, so I can recommend it for now.


1 comment:

  1. Those are very impressive schematics for rain harvesting and water catchment. It’s something to consider if some of your readers want to add one to their farms or as a backup water supply. Anyway, thanks for sharing your thoughts on the matter. Cheers!

    Bert Aguilar @ Rainfill Tanks

    ReplyDelete