Average daily rainfall data was used in the analysis (Figure 1(b)). Adopting a runoff coefficient of 0.8 for the iron roof (Thomas & Martinson 2007), the analysis was done for a population of 300. Even though it is a day school, all days of the year were included because other activities occasionally occur on weekend days and holidays. A simple daily water balance model by Mun & Han (2012) was adopted using the cumulative water storage (Equation (1)). Equations (2) and (3) represented daily demand and usage conditions.
1
2
3
where Vt is the cumulative rainwater stored in the tank (L) after the end of the tth day, Vt−1 is the stored rainwater in the tank (L) at the beginning of the tth day, Qt is the harvested rainwater (L) on the tth day, Ot is the overflow amount (L) on the tth day, Dt is the daily rainwater demand (L) on the tth day, Yt is the rainwater supplied (L) during the tth day, and S is the capacity of the rainwater tank (L).
Table 1

Cost breakdown of the Mnyundo school RWH demonstration project construction

S/NItem descriptionTotal (TZS)Total (US$) Storage tank and gutter profile system 3,170,500 1,962.55 First flush tank system 114,060 70.60 Foundation and base slab construction 1,008,000 623.96 Tap water system 284,000 175.80 Material transportation 420,000 259.98 Labor cost 820,000 507.58 Grand total 5,816,560 3,600 S/NItem descriptionTotal (TZS)Total (US$)
Storage tank and gutter profile system 3,170,500 1,962.55
First flush tank system 114,060 70.60
Foundation and base slab construction 1,008,000 623.96
Tap water system 284,000 175.80
Material transportation 420,000 259.98
Labor cost 820,000 507.58
Grand total 5,816,560 3,600
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