For design of sewers, percentage of sewage discharge is assumed

Solution (By Examveda Team)

Let's understand this question step by step.

Imagine water coming into your home from the city supply. You use this water for many things: bathing, cooking, flushing toilets, washing clothes, and so on.
The used water that goes down the drain and carries waste is called sewage. The underground pipes that collect and carry this sewage are called sewers.

Now, when civil engineers design these sewers, they need to know how much sewage they should expect to flow through the pipes so they can make them the correct size. If the pipes are too small, they will overflow. If they are too big, they will be expensive and not work efficiently.

Here's the key point: Not all the water supplied to a city or town becomes sewage.
Why? Because some water is:
- Drunk or used in food preparation and is consumed.
- Used for watering gardens and lawns, where it evaporates or soaks into the ground.
- Lost due to leakages in the water supply pipes before it even reaches homes.
- Used in some industrial processes where water is consumed and not discharged as wastewater.

So, engineers make an assumption about what percentage of the total water supplied will actually convert into sewage discharge.
This percentage helps them estimate the flow rate for designing the sewers.

Based on standard engineering practices and observations, it is generally assumed that about 70% to 80% of the total water supplied to an area will eventually become sewage and needs to be carried by the sewers.
Sometimes, this figure can be slightly adjusted based on the specific type of area (e.g., purely residential, commercial, or industrial), but 70-80% is a widely accepted range.

Looking at the given options:
Option A: 65 to 70%
Option B: 70 to 75%
Option C: 75 to 80%
Option D: 85%

The most appropriate and commonly assumed range for the design of sewers is 75 to 80%. This value ensures that the sewers are adequately sized to handle the expected sewage flow, considering the factors mentioned above.

Therefore, the correct answer is Option C: 75 to 80%.