For groundwater productivity, water points with moderate productivity have a higher failure likelihood in the full sample, those between 5 and 10 years old and those over 11 years using very low and low to moderate groundwater productivity water points as reference. On the other hand, water points with very high and high groundwater productivity have lower likelihood of failure in the first year, and higher likelihood at over 11 years. For groundwater storage, those with low medium groundwater storage has failure rates that are higher for the full sample, year 1 and those between 2 and 4 years old but are insignificant thereafter. For those with medium storage, they have a higher likelihood of failure for all cases, years 5-10 and over 11 years old. This result supports the findings from Fisher (2015) that water points with low groundwater storage are associated with higher functionality in general. There is clear evidence showing that hydrogeological factors are important predictors of water point failures as in the case of Andres et al. (2018) and Fisher (2015).

Finally, regarding depth to groundwater, using very shallow as reference, shallow groundwater was positive and significant at the one percent level for all groups suggesting higher failure rates, except those which are one year old and under, which was insignificant. The result was similar for those for which no values were available. Finally, shallow medium had higher failure rates for only those water points which are 2-4 years of age and those between 5 and ten years.

- _(c) Shapley Decomposition of Water Points’ Failure_

In this section, we use the results from logistic regression to calculate the contribution of various factors to the failure of water points (Table 7). We group together water points that are one year old, two to four years old, five to ten years old and over eleven years old to determine failure by age. The predicted effects of age, hydrogeology, localities, zones, pump types, promoter and management body in explaining the likelihood of water scheme failure in each of these three age groups, along with the Shapley values (Table 7) for each component’s contribution to failure, is calculated (Figure 16). The marginal contribution of pump type is at 58 percent for all water points for all age groups while age only accounts for 16 percent. The marginal contribution of hydrological factors accounts for 6 percent for all water points. During the first year, the marginal contribution of hydrological factors is the highest at 53 percent, thus accounting for more than half of all components. However, the contribution of components changes considerably by years 2-4. The pump type contributes more than half of the total when compared to all the other components, accounting for 54 percent and this increases sharply to 63 percent by year 5 to ten years old, and 70 percent for those over eleven years. There is no specific pattern regarding other components as the water points age although hydrological terrain still contribute ten percent of reasons for non-functionality for water points aged over five years. Type of promoters, localities and age make small contributions to failure. Type of management body is important for years 2-4, and thereafter its contribution declines significantly.

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