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Introduction

A water catchment system is a system used to capture clean water from rainfall and direct it into a storage container. It is an easy method of obtaining potable water and storing it for future use.

One of the requirements of a water catchment system is that they require a large exposed surface to collect water. Undoubtedly this large surface will be prone to collecting pollutants such as fecal coliforms, heavy metals (Zn, Pb, Cu, Cd, Cr, Ni), ammonia (NH4+), particulates, and other organic debris due to its direct exposure to the climate, heat, moisture, animals, etc. As the whole purpose of these RRCS’s is to deliver potable water to developing communities, it is crucial to reduce the level of these pollutants in the water before it is put into storage.

Polluted water can be very dangerous in communities where health care and sanity are generally neglected. Contaminated water can cause serious illness; acute affects range from diarrhea, nausea, vomiting and lung irritation, and chronic affects include cancer, birth defects and organ damage. Pollutants accumulate on the runoff surfaces over periods of no or little rain. This is why it is especially important to get rid of the pollutant build-up before the start of heavy rainfall or rainy season. In order to accomplish this effectively and inexpensively, the “first-flush” method is widely used.

This method uses rainwater to wash away materials accumulated on the collection surface before the run-off water is put into storage for potable use. The first water collected can be used to fertilize the land, but should not be consumed. There are a variety of factors which may affect the amount of pollutants that build up on the collection surface, and thus affect how much run-off water needs to be disposed of before being collected. Climate and geographic location play a large role in this, as this affects temperature, humidity, weather patterns, flora and fauna, etc. Generally there is greater ability for pollution built up in warm, tropical climates, as they are better breeding grounds for bacteria and organic debris. Geographic location, proximity to large pollution cities, can also affect the pH level of rain-water, and acid rain may react with the roof material and displace heavy metals into the water.

Rainfall intensity and frequency are also very important factors to examine when trying to determine first flush requirements. The harder it rains, the greater the force and thus it is easier to displace and flush away pollutants stuck to the collection surface. In addition, if it rains frequently, there is less chance for pollutants to build up on the surface between rainfalls. The material used for the collection surface is also very important. Metal roofs are more prone to heavy metal leakage when exposed to acid rain – however they are generally rather smooth and as such accumulate fewer particulate pollutants. Tile roofs have a coarser surface and tend to gather more pollutants. Due to these different possibilities, roof rainwater catchment systems need to be evaluated on a case by case basis.

Water Catchment

Every water catchment system has three basic parts:

1) The collection surface

2) The collection basin

3) The gutter system

The design of this optimized water catchment system focuses on the design of a first-flush system, which primarily encompasses the gutter system, and somewhat of the collection basin. The collection surface is briefly looked at, but the focus is on the requirements for a first-flush system.

It should also be noted that although a first-flush system is a great method of diverting the large contaminants from the main collection basin, there will still be some smaller contaminants that need to be filtered out before the water can be considered potable. To do this, a filtration device is required.

Collection Surfaces

Collection surfaces must have minimal opportunities for contamination, inert or essentially inert materials, a large surface area, and a design which ensures maximum water flow. The table below gives a basic outline of various roof materials that can be used for collection. Essentially, any roof that is not made of organic material can be used in a rainwater catchment system.

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Collection Basins

The only difference for a collection basin in a first flush system is that a second, smaller basin is needed for the diverted, non-potable water. The selection of the main storage basin is not important to making a first flush system work. However, there are many other considerations for choosing/designing a collection basin. The only purpose of a collection basin is to provide a container in which to store water for a significant amount of time. The additional factors to consider are whether the basin is above or below ground, and the shape. The following table provides a list of pros and cons for above vs. below ground collection basins.

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Gutter Systems

The gutter system is the most important aspect of a water catchment system that uses a first-flush approach to decontamination. The gutter system must direct the water from the collection surface to the collection basin. In a first-flush approach, the gutter system is also responsible for directing the non-potable water from the first rainfall to a separate collection basin.

The Proposed Design

The design of this water catchment system using the first-flush method of primary decontamination is relatively simple.