--- title: "Sources and factors of sanitary sewage" subject: "Sanitary Engineering" chapter: 2 key: "semester_6/sanitary_engineering:sources-factors-sanitary-sewage" source: https://www.bctengineer.com/q/semester_6/sanitary_engineering/sources-factors-sanitary-sewage site: BCT Engineering --- # Sources and factors of sanitary sewage Sanitary Engineering · Chapter 2: Quantity of Wastewater - Asked in: 2078 Chaitra, 4 marks; 2077 Chaitra, 2+2 marks; 2069 Bhadra, 4 marks (asked 3 times) - Video: [Environmental engineering 2-KTU Syllabus-Module 1-Chapter 1.3-Part 2](https://www.youtube.com/watch?v=148UnmyDqBw) — Civil Mentor - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_6/sanitary_engineering/sources-factors-sanitary-sewage - Whole chapter: https://www.bctengineer.com/md/semester_6/sanitary_engineering/chapter-2 ## Question List out the potential sources of sanitary sewage and discuss briefly the key factors affecting the quantity of sanitary sewage. ## Short answer Sanitary sewage originates from residential, commercial, institutional, and industrial areas, plus groundwater infiltration and illegal connections. Key quantity factors include population and growth rate, water supply rate (sewage ≈ 75–80% of supply), area type and living standards, private water sources, groundwater infiltration (5,000–15,000 L/day/km/cm diameter), unauthorized stormwater connections, seasonal variations, and water metering which reduces wastage. ## Answer **Sanitary sewage** is the wastewater from the sanitary fixtures and activities of homes, offices, institutions and (to some extent) industries. It consists of human excreta, bath and kitchen water and washing water. #### Potential sources 1. **Residential areas:** toilets, bathrooms, kitchens, washing; the largest part. 2. **Commercial buildings:** offices, hotels, restaurants, shops, markets. 3. **Institutions and public places:** schools, colleges, hospitals, bus parks, temples, public toilets. 4. **Industries:** sanitary wastes of workers and (after pretreatment) process waste. 5. **Infiltration:** groundwater entering through defective joints and cracks. 6. **Other:** illegal roof or yard drain connections and leakage from the water supply. #### Factors affecting the quantity - **Population and its growth:** more people, more sewage. The sewer is designed for the future population at the end of the design period. - **Rate of water supply:** sewage is about 75-80% of the water supplied; the rest is lost in lawn watering, evaporation, leakage and consumption. - **Type of area:** residential, commercial or industrial areas produce different flows; commercial and industrial areas have high per-hectare flows. - **Standard of living and habits:** in rich households, the use of flush toilets, washing machines and showers increases the flow. - **Private water supplies:** water from wells entering the sewer adds to the sewage that is not recorded by the public supply. - **Groundwater infiltration:** depends on the water table, sewer material, quality of joints and age; it can be 5,000-15,000 litres per day per km of sewer per cm diameter. - **Unauthorised connections:** storm water or other waters connected to the sewer. - **Climate and time variation:** hourly, daily and seasonal peaks; summer use is higher than winter use. - **Water meters and tariff:** metering reduces wastage, and so reduces sewage. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which is the largest source of sanitary sewage? A. Residential areas B. Industries C. Infiltration D. Public toilets Answer: A. Toilets, bathrooms, kitchens and washing in homes form the major part. (Key point: Sources) 2. About what fraction of the water supplied becomes sewage? A. 25-30% B. 50% C. 100% D. 75-80% Answer: D. The rest is lost in lawn watering, evaporation, leakage and consumption. (Key point: Water supply and sewage) 3. Why are sewers designed for the future population? A. Because sewage per head falls over time B. Because the flow increases as the population grows over the design period C. Because sewers cannot be enlarged cheaply and flow is constant D. Because the population has no effect Answer: B. Sewers must serve the population at the end of the design period. (Key point: Design population) 4. Groundwater infiltration into sewers depends on A. water table, sewer material, joint quality and age B. only the rainfall intensity C. only the sewer diameter D. the standard of living only Answer: A. Defective joints and a high water table let groundwater enter. (Key point: Infiltration) ## Related in Sanitary Engineering - [Factors affecting sewage; calculating discharge](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Afactors-sewage-calculate-discharge) — Sanitary Engineering, chapter 2 - [Estimating sewage quantity for a city](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aquantity-sewage-nepal-city) — 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 - [Factors affecting self-purification](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Aself-purification-factors) — Sanitary Engineering, chapter 6 - [Sewage sampling and BOD dilution method](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Asampling-bod-dilution) — Sanitary Engineering, chapter 5 - [Methods of sewage disposal](https://www.bctengineer.com/question.md?key=semester_6%2Fsanitary_engineering%3Amethods-sewage-disposal) — Sanitary Engineering, chapter 6 ## Related in other subjects - [Major sources and selection factors](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Asources-and-selection-factors) — Water Supply Engineering, chapter 2, asked 2× - [Water sources: quality and quantity](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Asources-quality-quantity) — Water Supply Engineering, chapter 2, asked 3× - [Rainfall-runoff relationship, factors affecting runoff](https://www.bctengineer.com/question.md?key=semester_5%2Fengineering_hydrology%3Arainfall-runoff-relation-factors) — Engineering Hydrology, chapter 4 - [Factors affecting water demand; variation](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Afactors-affecting-demand) — Water Supply Engineering, chapter 3, asked 5×