Design Flow TABLE 3.1: Typical Distribution of Per-Capita Water Demand Average use Category (L/d) (gal/d) Percent of total Residential 380 100 56 Commercial 115 17 Industrial 85 22 12 Public 65 17 9 Loss 40 11 6 Total 685 180 100 Source: Solley (1998). TABLE 3.2: Typical Demand Factors Demand Minimum Maximum Typical Daily average in maximum month 1.10 1.50 1.20 Daily average in maximum week 1.20 1.60 1.40 Maximum daily 1.50 3.00 1.80 Maximum hourly 2.00 4.00 3.25 Minimum hourly 0.20 0.60 0.30 Design Flow Component TABLE 3.7: Typical Design Periods and Capacities in Water Supply Systems 1. Source of supply: River Wellfield Reservoir Design period (years) Design capacity Indefinite Maximum daily demand 10-25 25-50 Maximum daily demand Average annual demand 2. Conveyance Intake conduit 25-50 Maximum daily demand Conduit to treatment plant 25-50 Maximum daily demand 3. Pumps: Low-lift 10 Maximum daily demand, one reserve unit High-lift 10 Maximum hourly demand, one reserve unit 4. Treatment plant 10-15 Maximum daily demand 5. Service reservoir 20-25 Working storage plus fire demand plus emergency storage 6. Distribution system (a) Supply pipe or conduit 25-50 (b) Distribution grid Full development Greater of (1) maximum daily demand plus fire demand, or (2) maximum hourly demand Same as for supply pipes Source: Gupta (2008) Design Flow: Example A metropolitan area has a population of 130,000 people with an average daily demand of 600 L/d/person. If the needed fire flow is 20,000 L/min, estimate: (a) the design capacities for the wellfield and the water-treatment plant; (b) the duration that the fire flow must be sustained and the volume of water that must be kept in the service reservoir in case of a fire; and (c) the design capacity of the main supply pipeline to the distribution system. 11