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Original:Slow sand filtration water treatment plants

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INTRODUCTION

The limited amounts invested in the treatment of safe water in rural areas are partly explained by the high cost of water treatment systems. Consequently, the majority of rural communities are still drinking superficial water that does not meet the required standard of quality, causing serious health problems.

In many cases, the high cost of water treatment systems and the poor quality of water deter investment in even the simplest systems of untreated water conveyance by gravity, further aggravating the health situation and forcing the population – particularly women and children – to walk long distances to fetch water of a worse quality than that which they could obtain by conveyance from the headwaters of nearby rivers.

Slow sand filtration systems are a technically viable water treatment solution. Nevertheless, there are still a number of difficulties involved in the implementation of the technology and the operation of the system. In addition, the direct cost of the construction is relatively high. A large percentage of these systems have been abandoned for the following reasons:

Inappropriate designs, as the variations in the quality of water at different times of the year were not taken into account.

The people in charge of operating them are usually members of the community who have not been adequately trained to operate the system.

The institutions responsible do not monitor the installations adequately.

Spare parts are not locally available.


The sand on the filter bed is not replaced when the minimum thickness has been reached, after several layers have been scraped off.


The main characteristic of slow sand filtration is that, due to the effect of biological activity, it efficiently removes pathogenic organisms from raw water, particularly the bacteria and viruses responsible for transmitting water-related diseases. Furthermore, no chemical products are required, nor highly qualified, continual supervision.

Slow filtration is undoubtedly the most adequate technology for rural areas. In order to avoid some of the problems described, however, it is necessary to apply solutions that take into account local technical and economic capacities, so that the system can actually achieve its purpose to supply drinking water to rural populations.

The proposal contained in this handbook is a low-cost alternative that is technically adequate and easily managed by the community. It consists of modified gravel pre-filtration, slow sand filtration and disinfection units adapted

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