Understanding Water Demand Variations and Peak Hourly Consumption

Water demand in a city or town is not constant throughout the day, month, or year. It varies significantly due to factors like time of day (morning peak, evening peak), season (higher in summer), day of the week, and special events. When designing water supply systems, engineers must account for these variations to ensure that enough water is available even during periods of highest demand.

Key terms related to water demand variations include:

• Average Daily Demand: The total annual water consumption divided by 365 days.
• Maximum Daily Demand: The highest amount of water consumed on any single day during the year. This is usually about 1.8 times the average daily demand.
• Peak Hourly Demand (or Maximum Hourly Consumption): The highest rate of water consumption during any one hour of the year. This typically occurs during specific hours of the day on the day of maximum consumption.

Water supply infrastructure, such as pipes and pumps, must be designed to meet the peak demands, not just the average demand. While pipelines might be designed for maximum daily demand and distribution reservoirs for peak hourly demand, the source and treatment plant capacity are often based on maximum daily demand.

Standard Factors for Peak Demand Calculation

Based on observations and studies, empirical factors are used to relate peak demands to average demands. Some common relationships are:

• Maximum Daily Demand is approximately \(1.8 \times \text{Average Daily Demand}\).
• Peak Hourly Demand is approximately \(2.7 \times \text{Average Daily Demand}\).
• Peak Hourly Demand is also often expressed in relation to the average rate of consumption on the maximum day. The average hourly rate on the maximum day is \( \frac{\text{Maximum Daily Demand}}{24} \). The Peak Hourly Demand is typically taken as \(1.5 \times \left( \frac{\text{Maximum Daily Demand}}{24} \right) \).

Analyzing the Options

The question asks about the maximum hourly consumption (Peak Hourly Demand) and provides options relating it to average daily demand or average hourly demand.

Let's look at the given options:

Options 2 and 4 use the term "average hourly demand". In the context of peak factors, "average hourly demand" when used with factors like 1.5 usually refers to the average rate of consumption specifically on the maximum day, which is calculated as Maximum Daily Demand divided by 24 hours (\( \frac{\text{Maximum Daily Demand}}{24} \)).

Considering this interpretation, Option 4 states that the maximum hourly consumption is \(1.5 \times \text{average hourly demand}\). If "average hourly demand" means the average rate on the maximum day (\( \frac{\text{Maximum Daily Demand}}{24} \)), then this option represents the relationship: \( \text{Peak Hourly Demand} = 1.5 \times \left( \frac{\text{Maximum Daily Demand}}{24} \right) \). This is a widely accepted standard factor for calculating peak hourly demand based on the peak day's average rate.

While Option 1 (\(2.7 \times \text{average daily demand}\)) is also a standard factor for peak hourly demand, the phrasing in Option 4, using the factor 1.5 multiplied by "average hourly demand" (interpreted as the average rate on the maximum day), is another common way to express and calculate peak hourly demand, and is provided as an option.

Therefore, based on standard water supply engineering practices and the options provided, the value \(1.5 \times \text{average hourly demand}\) (interpreting "average hourly demand" as the average rate on the maximum day) represents the maximum hourly consumption.