---
title: "Living organisms in water; health effects"
subject: "Water Supply Engineering"
chapter: 4
key: "semester_5/water_supply_engineering:living-organisms-in-water"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/living-organisms-in-water
site: BCT Engineering
---

# Living organisms in water; health effects

Water Supply Engineering · Chapter 4: Quality of Water

- Asked in: 2074 Asoj, 8 marks
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/living-organisms-in-water
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-4

## Question

Describe the various types of living organisms present in water. Discuss their effects on human health.

## Short answer

Water contains bacteria (cholera, typhoid), viruses (hepatitis, polio), protozoa (amoebic dysentery, giardia), helminths (worms), algae (toxins, taste/odour), fungi, and zooplankton (intermediate hosts, mosquito larvae). These cause diseases, taste/odour issues, and filter clogging. Control involves source protection, filtration, and disinfection.

## Answer

Natural water contains many living organisms; some are harmless, some are harmful and some give problems of taste and odour.

| Organism | Examples | Effects on human health / water supply |
|---|---|---|
| Bacteria | Vibrio cholerae, Salmonella typhi, Shigella, E. coli | Cholera, typhoid, dysentery, diarrhoea |
| Viruses | Hepatitis A and E viruses, polio virus, rotavirus | Jaundice, polio, diarrhoea |
| Protozoa | Entamoeba histolytica, Giardia lamblia, Cryptosporidium | Amoebic dysentery, giardiasis, cryptosporidiosis; cysts resist chlorine |
| Helminths (worms) | Ascaris, hookworm, Schistosoma, guinea worm | Worm infections, bilharzia, dracunculiasis |
| Algae | Blue-green algae (Microcystis), diatoms, green algae | Taste, odour, colour and clogging of filters; some algae produce toxins that affect liver and nerves |
| Fungi and actinomycetes | Moulds, yeasts | Earthy-musty taste and odour |
| Iron and sulphur bacteria | Crenothrix, Beggiatoa | Corrosion, red/black slime, bad smell |
| Zooplankton and small animals | Cyclops, water fleas, rotifers, snails, insect larvae | Intermediate hosts of parasites (Cyclops carries guinea worm); mosquito larvae grow into adults that spread malaria and dengue |

#### Control
Protect sources from sewage and runoff, control algae by copper sulphate or chlorine, provide filtration and disinfection (chlorination, UV, ozone), and cover storage tanks to prevent mosquito breeding.

## Check yourself

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

1. Protozoal cysts such as Giardia are notable because they:
   A. resist chlorine
   B. are killed by 1 mg/l instantly
   C. are only in sea water
   D. cause taste only
   Answer: A. Filtration or stronger disinfection is needed. (Key point: Protozoa)

2. Algae in water cause mainly:
   A. cholera
   B. taste, odour, colour, filter clogging and some toxins
   C. hepatitis
   D. bilharzia
   Answer: B. Blue-green algae toxins affect liver and nerves. (Key point: Algae)

3. Crenothrix and Beggiatoa cause:
   A. polio
   B. dysentery
   C. corrosion, slime and bad smell
   D. goitre
   Answer: C. They are iron and sulphur bacteria. (Key point: Iron bacteria)

4. Mosquito larvae in stored water spread:
   A. cholera and typhoid
   B. ascariasis
   C. fluorosis
   D. malaria and dengue
   Answer: D. Covering tanks prevents breeding. (Key point: Zooplankton)

5. Algae in reservoirs are controlled by:
   A. copper sulphate or chlorine
   B. lime only
   C. raising hardness
   D. sedimentation of bacteria
   Answer: A. Also protect sources from sewage. (Key point: Algae control)

6. Which are helminths?
   A. Vibrio, Shigella
   B. Ascaris, hookworm, Schistosoma
   C. Giardia, Entamoeba
   D. Rotavirus, polio
   Answer: B. Helminths are worms. (Key point: Helminths)

## Related in Water Supply Engineering

- [Indicator organisms and membrane tube fermentation](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aindicator-organisms-mtf) — Water Supply Engineering, chapter 4, asked 3×
- [Indicator organisms](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aindicator-organisms-definition) — Water Supply Engineering, chapter 4
- [Slow sand filter, 15000 present population](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Assf-c76) — Water Supply Engineering, chapter 6
- [Causes and effects of hardness](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-causes-effects) — Water Supply Engineering, chapter 4
- [Effects of hardness; zeolite softener](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-zeolite-softener) — Water Supply Engineering, chapter 6
- [Potable, wholesome water; function in body](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Adefine-potable-wholesome-function) — Water Supply Engineering, chapter 1

## Related in other subjects

- [Water pollution: sources and effects](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Awater-pollution-sources-effects) — Environment and Pollution Control, chapter 4
- [Water logging: causes, effects, remedies](https://www.bctengineer.com/question.md?key=semester_6%2Firrigation_and_drainage_engineering%3Awater-logging-causes-effects-remedies) — Irrigation and Drainage Engineering, chapter 9, asked 13×
- [Sources, effects and remedies of water pollution](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollution-sources) — Engineering Chemistry, chapter 3, asked 2×
- [Water pollution, pollutants and adverse effects](https://www.bctengineer.com/question.md?key=semester_2%2Fengineering_chemistry%3Awater-pollutants-effects) — Engineering Chemistry, chapter 3