Surface Catchment

I first encountered this system in Nicaragua in 1973, while part of a relief team sent there after the devastating earthquake in Managua, the capitol.

Our team was given the use of a caretaker's house on a coffee plantation, miles from the nearest village, Jinotepe. Well-drilling technology was not used by villagers; they caught the monsoon rains. Our house had such a surface-catchment system, and it worked beautifully. Here's how:

There was a large catchment surface, about 35 feet square, made from a thin layer of concrete on the flattened earth, very smooth, with maybe a two-inch wall all around, possibly concrete-covered bricks. This catchment sloped gradually toward a large underground tank or cistern, called a 'pila', which was at one corner of the lowest edge. A simple coarse screen kept out leaves, as the water simply flowed from the catchment through a hole in the side of the short wall surrounding the pila.

Built on this wall, which was perhaps 18" high, was a wooden-framed structure, supporting a corrugated metal roof and screened all around with window screen. A small hinged door in the roof allowed one to drop a bucket on a rope and pull up water. Water for washing, bathing, drinking, cooking - one water source for everything.

The cistern or pila was about 10' in diameter and perhaps 15' deep. The three-year drought ended while we were there, and in preparation for the rain, the caretakers cleaned the pila, which was nearly empty. First, they saved all the water they could in barrels, then they took the roof apart. A man was lowered on a rope seat, and he passed bucket after bucket of sludge up to relatives who used it to compost the garden. The concrete pila was soon spotless, then the roof was put back on - usually a yearly ritual.

Talk about timing. These villagers can smell rain or sense it days in advance. Hardly a week had passed when the monsoon rains began, and what a downpour a monsoon rain can be! I stood in the warm rain on the catchment, watching the system in action. The pila roof slopes toward the catchment, obviously, and adds to the torrent of water flowing into the pila. I was amazed how fast a heavy rain can fill that tank.

How to keep water fresh all year. This pila system had four features that helped keep water drinkable: 1) The water was cold, deep in the ground. 2) The water was free of organic matter, due to the fine screening. 3) The water was airated, having a large surface area exposed to fresh air. 4) The water was kept dark, discouraging algae. Remember: cold, clean, airated and dark.

Anatomy of a gringo's surface catchment system. Here in the US, the labor required to dig a large tank in the ground and surface it with concrete might be a reason few people do that. What many people use are polyethylene tanks, because they are certified for drinking water, and they are relatively inexpensive - between $0.50 and $1.00 per gallon of storage capacity.

Here is an almost ideal situation: The catchment is above the storage tank. In fact, if there is enough elevation, one can include a settling tank below the catchment - a sort of huge drop filter. This in-between tank holds one heavy rain, and while holding it, silt and other suspended particles settle to the bottom. Open a valve and the clear water flows by gravity to the storage tank. Then you rinse the tank of sediment and it's ready for the next rain.

The storage tank sits below the settling tank and far enough above the house to provide adequate water pressure by gravity. What is adequate? Siphon water out of a bucket with a hose and see what you consider adequate. My tank is 15' above my house and I have more than adequate pressure. Make sure your feed pipe is large, like 2" diameter, from tank to house, to limit friction.

This system is almost ideal, because the tanks are above ground where they will become warm in the sun, heating the water inside, which could encourage algae. Painting the dark tanks with light-colored paint helps keep them cooler. Some people build lightweight frames over and around the tank to shade it.

This entire system operates with no power. Gravity does all the moving of water, and it even creates enough water pressure for household use. This kind of system requires gently-sloping land or terraces. Here's one of mine:

New Catchment with Pipe to tank

This 1260 sq. ft. catchment is still dirt. The 2" pipe to the tank is being burried. Once the catchment's surface is smooth and rolled flat, the chicken wire and concrete go on.

Surfacing a Catchment with concrete

Plastic sheeting keeps the concrete sections wet to cure hard. The burried pipe is plumbed to the tank below.

Tank and catcment

To make periodic cleaning easier, a repair coupler is inserted between the pipe and the tank, so they can be disconnected.

Big tank

And speaking of cleaning a tank...

Cleaning large tank

It's risky to climb down into a large tank, because it's nearly impossible to get back out. So I tip mine on its side and climb in backwards. Honeybees love water and join me inside, making quite a racket. Many perish in the heat - it was a sunny day - ending up in the wash water lower right.

For a higher and smaller catchment, I have two tanks plumbed together. Overflow from the upper one fills the lower one. Both can be tapped for domestic water (house). In the photo below, the lower tank still receives water from the catchment, because I have just added the upper tank. Catchment water now goes to the upper tank, overflow to the lower tank.

Twin tanks

Using a gas torch, I heat and soften the pipe from the upper tank and wrap it around the lower one, then connect the two tanks together, with valves (one shown) to select which feeds the house. The garden hose (pictured) was temporary and has been replaced by a repair coupler, joining the tank with the pipe to my house. I can now use water from either tank.Twin tanks plumbed together

The dual-tank system has several big advantages over a single tank.  1) If somebody leaves a valve open or the system has a leak, I may lose all the water from a tank, but I have a backup tank full of water. A single tank system can lose everything. 2) Fresh water entering a tank stirs the sludge on the bottom, making all the water cloudy. By using water from one tank while the other receives water, I always have clear water. 3) I can also clean one while the other is online - very convenient, and no interruption of my water supply.

Backing up a bit, here is how I created places for tanks - cut into the hillside and make a firm level pad. Be sure the tank sits on 'cut' and not on 'fill', which will settle.

Level spot for tank

But let's back up further. How did I get the tanks to my land? You may not want to try this at home...

Rolling first tank

Since there is no road to my land, I had to roll my tanks several miles, and that was the easy part! From this river to my land is another two and a half miles up a dry wash.

Tank on water fall

On the way, there are lots of, um, obstacles, like this waterfall and endless huge boulders. This was the first of three tanks, and it's the smaller one. However, as the photos above show, I did get all three tanks in place, eventually.

If you have the land, a surface system can provide you with plenty of clean water all year. There is little maintenance, and once the system is installed, your water is free. Another bonus is that the entire system can operate without power. Gravity does all the work. No water bill, no electric bill.

Overflow must be managed to avoid erosion. Tanks have an overflow opening near the top. When the tank fills to that level, more water entering will flow out. Connect a pipe to this threaded outlet and direct overflow water someplace where it can do some good, like to fill another tank or water some trees. What you want to avoid is water flowing down the tank, as it can erode the tank's support and carry away soil.

 DVD Soon!

Watch this space for the coming DVD on how to install your own rainwater harvesting system.