---
title: "Differentiate DWF and WWF; sources"
subject: "Sanitary Engineering"
chapter: 2
key: "semester_6/sanitary_engineering:dwf-wwf-sources-sewage"
source: https://www.bctengineer.com/q/semester_6/sanitary_engineering/dwf-wwf-sources-sewage
site: BCT Engineering
---

# Differentiate DWF and WWF; sources

Sanitary Engineering · Chapter 2: Quantity of Wastewater

- Asked in: 2071 Bhadra, 4 marks
- Video: [QUANTITY OF SEWAGE: DRY WEATHER FLOW AND STORM WATER FLOW, PART 35, ENVIRONMENTAL ENGINEERING](https://www.youtube.com/watch?v=j2oP6DvTj24) — Vidhya Focus-2020
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_6/sanitary_engineering/dwf-wwf-sources-sewage
- Whole chapter: https://www.bctengineer.com/md/semester_6/sanitary_engineering/chapter-2

## Question

Differentiate dry weather flow and wet weather flow. Briefly describe various sources of sanitary sewage.

## Short answer

DWF is flow without rain, small and steady; WWF is flow during rain, much larger and variable. Sources of sanitary sewage include residential buildings (toilets, kitchens, baths), commercial and institutional establishments, industrial sanitary waste, public places, and groundwater infiltration.

## Answer

#### Difference between DWF and WWF
| Point | Dry weather flow (DWF) | Wet weather flow (WWF) |
|---|---|---|
| Meaning | Flow in sewer without rain | Flow in sewer during or after rain |
| Components | Domestic + industrial sewage + infiltration | DWF + storm runoff |
| Magnitude | Small and fairly steady | Many times greater, highly variable |
| Duration | Always present | Only during rain |
| Use in design | Minimum velocity check, treatment plant, separate sewers | Capacity of combined and partially separate sewers, overflows |
| Estimation | Population x per-capita flow x peak factor | DWF + $CiA/360$ |

#### Sources of sanitary sewage
1. **Residential:** water closets, bathrooms, kitchens and laundry. This is the main source.
2. **Commercial:** offices, hotels, restaurants, markets, shops.
3. **Institutional:** schools, hospitals, colleges, hostels, public buildings.
4. **Industrial:** sanitary wastes of employees, and process wastes where allowed.
5. **Public places:** public toilets, bus parks, parks.
6. **Groundwater infiltration** through leaking joints and manholes, and **unauthorised connections** such as roof drains.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. Which statement correctly differentiates DWF and WWF?
   A. DWF occurs only during rain
   B. WWF is small and steady
   C. DWF is the flow without rain, while WWF is DWF plus storm runoff
   D. Both have the same magnitude
   Answer: C. WWF is many times larger and highly variable. (Key point: DWF vs WWF)

2. WWF is used mainly to decide
   A. capacity of combined and partially separate sewers and overflows
   B. the minimum velocity
   C. the per-capita water supply
   D. the number of houses
   Answer: A. DWF is used for the minimum velocity check and the plant. (Key point: Use in design)

3. Which is the main source of sanitary sewage?
   A. Bus parks
   B. Industries
   C. Residential: closets, bathrooms, kitchens, laundry
   D. Hospitals
   Answer: C. Residential areas contribute most of the sewage. (Key point: Sources)

4. Which of these adds to sewage flow but is not intended?
   A. Toilets
   B. Groundwater infiltration and unauthorised roof drain connections
   C. Kitchens
   D. Laundry
   Answer: B. Leaking joints and illegal connections add unwanted flow. (Key point: Extra flows)

## Related in Sanitary Engineering

- [Define DWF, WWF; estimating WWF](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Adwf-wwf-quantity-wwf) — Sanitary Engineering, chapter 2
- [Sources and factors of sanitary sewage](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asources-factors-sanitary-sewage) — Sanitary Engineering, chapter 2, asked 3×
- [DWF and WWF in sewer design](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Adwf-wwf-importance) — Sanitary Engineering, chapter 2
- [DWF, WWF and storm water factors](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Adwf-wwf-storm-factors) — Sanitary Engineering, chapter 2
- [Wet weather discharge, combined sewer](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Awet-weather-discharge-small-town) — Sanitary Engineering, chapter 2
- [Sources of sewage and city impact](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asources-sewage-impact-city) — Sanitary Engineering, chapter 2

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