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It is important to remember that all selection criteria must be measurable. The whole purpose of the exercise is to make selection as objective as possible and minimize subjective decisionmaking. Criteria such as 'consumer demand' should only be used if based on a consumer survey carried out and analysed by a competent organization. The following criteria could form a basis for project selection. |
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3.2.1
Projected Total Population |
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Schemes expected to serve large populations at the end of the design life are generally considered to have a higher priority than those with a lower projected population. This is because large schemes tend to have a lower per capita cost, produce greater social and environmental gains, maximize the number of people having access to improved sanitation and improve the local environment through reductions in odour and inconvenience from open sullage drains. |
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Generally, the higher the population density, the greater the health hazard from poor sanitation and the lower the unit cost of sewerage. Also, as housing density increases and plot sizes decrease the chances of on-site sanitation systems failing increases. |
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3.2.3
Failure of On-Site Sanitation Systems |
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The most common types of on-site system are pit latrines (of varying types) and septic tanks. Readers are advised to consult Franceys et al. (1992) for details of the design and construction of such systems. |
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The failure of existing on-site sanitation systems is one of the commonest reasons given for needing sewerage. As sewerage is far more expensive than on-site sanitation the planner should check the causes of any failure (current or projected) before altering the status quo. In many cases failure occurs because of |
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