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
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.
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
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
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
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
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:
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.
Plastic sheeting keeps
the concrete sections wet to cure hard. The burried
pipe is plumbed to the tank below.
To make periodic
cleaning easier, a repair coupler is inserted between
the pipe and the tank, so they can be disconnected.
And speaking of cleaning a
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.
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
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.
But let's back up
further. How did I get the tanks to my land? You may
not want to try this at home...
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.
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.