Typical Water Demand Chart for a Small Community
Water Demand for domestic consumption is normally termed as Average Daily Demand (ADD). The Peak Daily Demand
(PDD) is normally taken as 1.2 x Average Daily Demand. And the Peak Hourly Demand (PHD) is taken as 2 x the Peak
Average Daily Demand is consumption in gals/day or lits/day averaged over a 12 month period. For eg, for
domestic usage the water demand can range from a high of 50 gals/person/day to a low of 25 gals/person/day
depending on which countries and population. Usually for design purpose, an average data is used such as 40
gals/person/day. The reader is advised to check with the Local Authorities on their own design requirements.
PDD = 1.2 x ADD
PHD = 2 x PDD
What this means is that the Water Demand from a community range from a minimum to a maximum peak which can be
2.4 x the Average Daily Rate. This can be demonstrated by the above Chart which measures a 24 hrs water
demand from a small community. This is a one day water demand and note the wide fluctuation of pressures
in the pipelines. The lower is the pressure, the higher is the demand and it corresponds to around 7:45am,
1:00pm, and 8:40pm in this community. While the periods around 4am, 11am, and 3pm require less water demand,
corresponding to the community out at work.
Thus when you design for Pipeline Hydraulics and Storage Capacity of Water Tanks, these fluctuating demand
should be taken into careful considerations, so that an economical solution can be made.
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Authur- Philip Goh (B.Sc, MIEM, P.Eng. MICE,
MEC Engineers, Civil & Structural Engineer