Rainwater Catchment

What is Rainwater Catchment?

The rainwater cistern is historically an underground basin of water, but it can also be an above ground barrel or tank. Much like an artificial well, cisterns are used to make sure that water is not contaminated nor suffers from evaporation. Probably the most effective but overlooked form of rainwater storage in the modern era rainwater cisterns are practical and can be aesthetically concealed below ground, behind fencing or trellis. Good materials for cisterns include plastic liners or membrane material in wood frames, ceramic, fiberglass, “food grade” plastic and poly-tanks, as well as other potable liquid materials.

The two main reasons why people use cisterns are either for the sake of survival in a place where the only potable water is rainwater, or ecological awareness in search of sustainability. Either people need a cistern, or want one because they are concerned about how they (or others) are consuming water. A rainwater basin needs to offer enough capacity to collect enough useable water from a catchment surface. Rain barrels are exceptional tools for not only excess cistern water, but if connected together can catch enough rainwater to filter for using for cabins and other weekend getaways.

The rainwater cistern can hold large amounts of water and is completely sealed from contaminants, except those in the water itself. Where evaporation and external contamination can be issues with basins, the most practical thing about a cistern in all this is both size and location. Historically cisterns are put underground because it is one of the safest places to put something that is to be kept under constant temperature. Nowadays, we have giant rainwater cisterns that can be bought from manufacturers and become a wonderful element to add to your backyard, or barn, there is no reason not to be proud your rainwater harvesting tank.

Accumulated water is wealth in some places, and among the people of the sand in Africa, water is synonym for the word God, so important is this natural resource. Eskimos have more than 30 different words for snow, so important is it in their way of life.

In the average American family of four, anywhere from 900 to 1200 liters of water are consumed daily. So much water, what if it doesn’t rain for six months? Well, calculate the amount of cubic liters needed to safely use a cistern year round according to catchment size, rainfall, and daily consumption. The longest dry season, will determine the longest length of time without water, and that multiplied by days and liters would give the total size of any given rainwater cistern.Rainwater catchment is the term used to describe any system that acts as a kind of sky net to capture and impound rainfall. What exactly is it that can be a rainwater catchment system? Are catchments strictly artificial, or can they be found in Nature as well? What about today? In today’s world, what is it that can be considered a catchment? Are there more common types of catchments that have been used throughout history, and what is most common today? What about the term efficiency? What is the efficiency of a rainwater catchment system?

The very earth itself in this definition of “rainwater catchment” works as one giant rainwater catchment system sustained by plentiful mountains and valleys across the many continents. The sky is so important to civilization, so omnipotent, that it has even become the foundation for hundreds of thousands of millions of different polytheisms since the dawn of humankind. Oxumare, the afro-brazilian goddess of rain and the rainbow is said to be a monster for six months out of the year and a beautiful woman named Bessem the other six. Probably due to the way the ancient African Jeje people would deal with rain, six months rainy season and six months dry season.

It is no wonder the etymological origin of the word catchment reconstructs mental images of “the hunt” and the animal being caught. As if a net were being furled like a sail in a horizontal fashion in expectation of the falling monster Oxumare who then replenishes the body to give life and beauty as when the rainbow appears after a storm and the smell of steam rises from the intense spring heat which evaporates upon the leaves and forms dense clouds of condensation upon flower petals and gently roll down into the center.

During the heavy rain the mountain remains firm and solid forming rivers down its side into gullies and ditches that eventually take to underground reservoirs and rivers into springs and surface going rivers that run for miles and miles to finally find their way to the everlasting sea. Yet in the sea as well, Oxumare finds her monstery form and then settles into the gentle rocking of mother Yemanja (goddess of the sea).

We humans make reasons for these things that happen in nature. And we imitate. Rainwater catchments in today’s reality no longer accept the poetic explanations of our primitive ancestors. Now things are based on the logic of a new and superior god known unto all as SCIENCE. It is HE who defines the truth, and it is He who tells us how a catchment system should be. Mostly, they are but imitations of the mountain top, the valley, gullies, underground reservoirs, rivers and springs.

Look closely at the roof of any house, or at the shape of rainwater harvesting cistern’s lid, and the whole mystery is reviled. Just a few things however need to be understood about the rainwater catchment system as a whole when used on roofs. First the catchment area, the area is the space on the roof that water hits. This includes the overhang and the gutters. The gutters organize the flow of water caught by the roof, and direct it into a downspout, where it is filtered like a kitchen sink drain and then finally stored in a barrel, or any other collection recipient. All of these elements make up the rainwater catchment system, area, gutters, downspout and reservoir. It’s a very simple process and any household can implement one with a little bit of common sense and start making use of roof in this fashion.

Not all rainwater catchment systems are roofs on top of houses as mentioned, some are surface water catchment systems for fields to improve irrigation. But essentially all of them need these four elements: AREA, SLOPE, DRAIN and STORAGE. Area, gives the water a place to land. Slope gives it gravitational pull, so that it can pick up speed and momentum, thereby flowing toward the drain. Drain, channels rainwater in an organized fashion so that it can actually form a consistent body. Storage is the final resting place for the flowing bodies of water that come from the drain. Stored water can then be used for any variety of daily needs, baths, dishes, plants, animals, drinking (when clean enough).

Another interesting factor in the development of any rainwater catchment system is taking into account the efficiency of the system as a whole. Efficiency is a term that refers to the amount of water lost in the process from the time the water first hit the collection area to the time it finds its way into storage. Water collection efficiency in this sense, is more related to water that goes flying away from the system, or escapes in some way, before reaching storage, such as in the case of too much slope and the water over shoots the drain. When water hits the overhang near the edge, the velocity is usually so high that not all of it is collected by the slope, and also ends up lost. Faulty gutters are another reason for rainwater catchment efficiency loss, improperly installed downspouts, mechanical filters that are just stuffed with debris can be a problem as well. Seepage, evaporation and contamination are also efficiency factors, but have more to do with rainwater harvesting in the general sense, rather than the catchment system itself.

As the catchment system is meant to simply hunt and capture the water as in times of old, when water had to be found for the gathering tribe to survive. Rainwater catchment systems today try to imitate nature as if hunting a primitive monster. In nature, mountains, land, even the sea, are all forms of collecting and storing rainwater, but in urban dwellings, the roof, the gutters and a barrel can do the same job, for one family. In cities, rivers are dammed and community reservoirs distribute water for the whole population. On farms they can capture water from the barn roof or just an enormous cistern. All systems revolve around the concept of efficiency. Especially household rainwater catchments, as they must be carefully calculated in order to be more useful, that is more efficient (water lost is water unused). Water is a gift to us, to all creatures on the earth. We must learn to use it efficiently and responsibly if we want to see a more sustainable future for those who will inherit this earth.


Posted in Harvesting by Administrator on September 9, 2005.

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