Water Supply and Waste Water Engineering MCQ With Answers for JKSSB Junior Engineer (Civil)

Technical · 2026-10-27 · 6 min read

Water supply and waste water engineering carried 10 marks in the board's earlier Junior Engineer (Civil) syllabus. It lists the quantity and quality of water, water treatment, conveyance, laying of pipes, building water supply and plumbing, sewerage systems, sewage characteristics and treatment, building drainage, and air and noise pollution. Because many of the 2026 posts are in the Jal Shakti Department, this subject is worth steady revision. The board's 2025 paper had 120 one-mark questions in 120 minutes. Our guide to the 2026 notice shows where this section fits. This page gives a revision list, worked problems and solved MCQs.

Quick revision list

  • Demand: per capita demand in litres per head per day, peak factors, and population forecasting methods such as arithmetic increase
  • Quality: turbidity, hardness, pH, dissolved oxygen, and the standard for drinking water
  • Treatment: screening, sedimentation, coagulation with alum, filtration (slow and rapid sand filters) and disinfection by chlorine
  • Sedimentation: overflow rate = Q ÷ A and detention time = V ÷ Q
  • Distribution: pipe materials, valves, service reservoirs and pipe laying
  • Sewerage: separate, combined and partially separate systems, self-cleansing velocity and manholes
  • Sewage: BOD, COD, dissolved oxygen, and disposal by dilution or on land
  • Treatment of sewage: primary treatment, trickling filters, the activated sludge process, sludge digestion and septic tanks
  • Pollution: air pollutants and noise measured in decibels

Worked numerical problems

  • Water demand: a town of 20,000 people at 135 litres per head per day needs 20,000 × 135 = 2.7 million litres a day, or 2.7 MLD
  • Overflow rate: a settling tank handling 1,200 m³/day with a surface area of 30 m² has an overflow rate of 1,200 ÷ 30 = 40 m³/m²/day
  • Detention time: a tank of volume 300 m³ receiving 1,200 m³/day has a detention time of 300 ÷ 1,200 = 0.25 day, or 6 hours
  • Population forecast: a town of 50,000 whose population grows by 4,000 in every decade will have 50,000 + 2 × 4,000 = 58,000 after 20 years by the arithmetic increase method
  • Rapid sand filter rate: a filter of 40 m² working at 4,000 litres per hour per square metre passes 160,000 litres an hour
  • Alum dose: a dose of 20 mg/L for a flow of 5 million litres a day uses 20 × 5 = 100 kg of alum a day

Treatment and sewage in brief

Raw water is first screened, then settled. A coagulant such as alum makes the fine suspended particles clump together into flocs that settle in the sedimentation tank. The water then passes through a filter, and a slow sand filter relies on a biological layer on its surface and works at a low rate, while a rapid sand filter works at a much higher rate and is cleaned by backwashing. Chlorine is added at the end to kill pathogens, and some chlorine must remain as residual to protect the water in the pipes. In sewage treatment, primary settling removes solids, secondary treatment such as the activated sludge process uses bacteria to break down the organic matter, and the sludge is digested to produce gas.

Common mistakes

  • Confusing the overflow rate (Q ÷ A) with the detention time (V ÷ Q)
  • Forgetting that BOD is measured over 5 days at 20°C
  • Mixing up slow and rapid sand filters: the slow filter works at the lower rate
  • Treating pH 7 as the only acceptable value, when the standard allows a range

Distribution and plumbing in brief

Treated water is stored in a service reservoir that balances the hourly variation of demand and keeps a reserve for fire fighting. It is carried through a network of pipes, laid in a grid in a town with many streets, so that water can reach any point from more than one side. Valves isolate a section for repair, and the pipes are tested for leaks before use. Inside a building, taps and fixtures are supplied by a branch from the main, with a stop cock at the entry.

Practise

Work the solved questions below, then read the Junior Engineer (Civil) guide for the dates and the marks for every subject. The other subject pages in this series cover irrigation, highway engineering, railway engineering and construction management.

By Shivam · Written with AI assistance and fact-checked · Questions on this page are original · Editorial policy · Report an error

Practice questions

Q1. The common coagulant used in water treatment is:

  1. Quicklime only
  2. Alum
  3. Bleaching powder
  4. Sodium chloride
Show answer

Alum — Aluminium sulphate makes fine particles clump together into flocs.

Q2. The main purpose of sedimentation in water treatment is to remove:

  1. Suspended solids that settle under gravity
  2. Dissolved salts
  3. Bacteria completely
  4. Hardness
Show answer

Suspended solids that settle under gravity — Settling lowers the load on the filters.

Q3. The overflow rate of a settling tank is:

  1. Volume divided by discharge
  2. Discharge divided by volume
  3. Surface area divided by discharge
  4. Discharge divided by surface area
Show answer

Discharge divided by surface area — Overflow rate = Q ÷ A, in m³/m²/day.

Q4. The detention time of a tank is:

  1. Discharge divided by volume
  2. Surface area divided by discharge
  3. Volume divided by discharge
  4. Discharge multiplied by volume
Show answer

Volume divided by discharge — t = V ÷ Q.

Q5. A settling tank of volume 300 m³ receives 1,200 m³/day. The detention time is:

  1. 4 hours
  2. 6 hours
  3. 12 hours
  4. 24 hours
Show answer

6 hours — 300 ÷ 1,200 = 0.25 day = 6 hours.

Q6. The overflow rate of a tank handling 1,200 m³/day with a surface area of 30 m² is:

  1. 40 m³/m²/day
  2. 36 m³/m²/day
  3. 400 m³/m²/day
  4. 4 m³/m²/day
Show answer

40 m³/m²/day — 1,200 ÷ 30 = 40.

Q7. A town of 20,000 people with a demand of 135 litres per head per day needs:

  1. 27 MLD
  2. 0.27 MLD
  3. 13.5 MLD
  4. 2.7 MLD
Show answer

2.7 MLD — 20,000 × 135 = 2,700,000 litres per day.

Q8. The rapid sand filter is cleaned by:

  1. Scraping the top layer only
  2. Adding alum
  3. Backwashing
  4. Draining it for a month
Show answer

Backwashing — Water is forced upward through the bed to wash away the trapped solids.

Q9. A slow sand filter works at a:

  1. Higher rate than a rapid sand filter
  2. Lower rate than a rapid sand filter
  3. Rate that needs a coagulant
  4. Rate that needs pressure
Show answer

Lower rate than a rapid sand filter — It relies on a biological layer on the surface and works at a low rate.

Q10. The most common method of disinfecting municipal water is:

  1. Chlorination
  2. Boiling
  3. Alum dosing
  4. Sedimentation
Show answer

Chlorination — Chlorine kills pathogens and leaves a residual in the distribution system.

Q11. The pH of drinking water should preferably lie between:

  1. 4.0 and 6.0
  2. 9.0 and 11.0
  3. 2.0 and 4.0
  4. 6.5 and 8.5
Show answer

6.5 and 8.5 — This is the acceptable range in the drinking water standard.

Q12. The hardness of water is mainly caused by dissolved salts of:

  1. Sodium and potassium
  2. Iron and copper
  3. Calcium and magnesium
  4. Chlorine and fluorine
Show answer

Calcium and magnesium — It is expressed in mg/L as CaCO₃.

Q13. The BOD of sewage is normally measured over:

  1. 1 day at 37°C
  2. 5 days at 20°C
  3. 10 days at 20°C
  4. 5 days at 37°C
Show answer

5 days at 20°C — BOD₅ at 20°C is the standard test.

Q14. A sewerage system that carries sewage and storm water in the same pipe is called:

  1. A combined system
  2. A separate system
  3. A partially separate system
  4. A septic system
Show answer

A combined system — A separate system uses two sets of pipes.

Q15. The minimum velocity in a sewer that prevents the deposition of solids is called the:

  1. Critical velocity
  2. Terminal velocity
  3. Settling velocity
  4. Self-cleansing velocity
Show answer

Self-cleansing velocity — A sanitary sewer is designed to run at about 0.6 m/s or more at its design flow.

Q16. The activated sludge process is a:

  1. Disinfection method
  2. Primary sedimentation method
  3. Secondary biological treatment of sewage
  4. Method of sludge drying only
Show answer

Secondary biological treatment of sewage — Bacteria break down the organic matter in an aerated tank.

Q17. Gas produced by the digestion of sewage sludge is mainly:

  1. Oxygen
  2. Methane
  3. Chlorine
  4. Nitrogen only
Show answer

Methane — It can be used as fuel.

Q18. A population of 50,000 grows by 4,000 in each decade. By the arithmetic increase method the population after 20 years is:

  1. 58,000
  2. 54,000
  3. 62,000
  4. 66,000
Show answer

58,000 — 50,000 + 2 × 4,000 = 58,000.

Q19. The unit used to express the loudness of noise is the:

  1. Pascal
  2. Hertz
  3. Lux
  4. Decibel
Show answer

Decibel — Noise levels are measured in decibels, dB.

Q20. A septic tank is used for:

  1. Treating the sewage of a large city
  2. Storing drinking water
  3. Treating sewage from a single house or a small group
  4. Collecting rainwater
Show answer

Treating sewage from a single house or a small group — The sludge settles and is digested in the tank, and the effluent is sent to a soak pit.

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