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Although obvious, the assumption was that greywater quantity generation rates measured directly from the field are more accurate than estimates given by household surveys. Since no statistically significant differences existed between the means of actual field greywater generation rates, the overall mean (43.36 ± 17 lpcd) was therefore taken as the test (true) value and compared with households' estimates. From the one-sample t-test (Table 2), there is a statistically significant difference between the field measured greywater generation rates and those estimated by households via surveys. The households overestimated the greywater generation rates by an average of about 8 lpcd, and this difference lies between 95% CI of 2–13 lpcd. When the test value is taken as the existing greywater generation rate (43.36 lpcd) for the study communities, the greywater quantity is about 36% of respondents' average water consumption (120 lpcd). This study reveals a higher greywater generation rate than the estimates of 18.8–25 lpcd provided by a recent study (Hyde & Maradza 2013). However, the greywater quantity in the current study represents a fraction (36%) of total water consumption, far below the known levels of 50–80%. This could be due to the limited sample size and/or because there is less greywater quantity generation during weekdays than at weekends. However, the greywater quantity generated in the study sites could be enough for reuse purposes such as toilet and urinal flushing within dwellings and this could reduce water demand by at least 30–38% (Al-Jayyousi 2003; Jefferson et al. 2004; Gisi et al. 2016).

Table 2

One-sample t-test for actual field and households' estimated greywater quantity

Test value = 43.36 lpcd
tdfSig. (2-tailed)Mean difference95% confidence interval of the difference
LowerUpper
2.765 89 0.007 7.8182 2.200 13.436 
Test value = 43.36 lpcd
tdfSig. (2-tailed)Mean difference95% confidence interval of the difference
LowerUpper
2.765 89 0.007 7.8182 2.200 13.436 

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