---
title: "Causes and effects of hardness"
subject: "Water Supply Engineering"
chapter: 4
key: "semester_5/water_supply_engineering:hardness-causes-effects"
source: https://www.bctengineer.com/q/semester_5/water_supply_engineering/hardness-causes-effects
site: BCT Engineering
---

# Causes and effects of hardness

Water Supply Engineering · Chapter 4: Quality of Water

- Asked in: 2079 Bhadra, 2 marks
- Video: [Hardness of water | types of hardness | engineering chemistry | water treatment | water softening](https://www.youtube.com/watch?v=jM_2mP_1NgI) — Digitech education
- Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/water_supply_engineering/hardness-causes-effects
- Whole chapter: https://www.bctengineer.com/md/semester_5/water_supply_engineering/chapter-4

## Question

Describe the causes and effects of hardness in relation to water supply systems.

## Short answer

Hardness is caused by dissolved calcium and magnesium salts. It wastes soap, forms scale in boilers and pipes, clogs pipes, imparts bad taste, and hinders cooking and industrial processes.

## Answer

**Hardness** is the property of water that prevents soap from lathering and causes scale in pipes and boilers. It is caused by dissolved salts of calcium and magnesium (and sometimes iron, strontium and manganese).

#### Causes
- Bicarbonates of Ca and Mg cause temporary (carbonate) hardness, which is removed by boiling.
- Sulphates, chlorides and nitrates of Ca and Mg cause permanent (non-carbonate) hardness.
- Water dissolves these salts when it passes through limestone, dolomite, chalk and gypsum rocks, so ground water is generally harder than surface water.

#### Effects
- Wastes soap, since hard water forms scum with soap before a lather forms; more soap and detergent are needed.
- Forms scale in boilers, hot water pipes, kettles and heat exchangers, reducing efficiency and sometimes causing explosion.
- Causes clogging of pipes and reduction of carrying capacity.
- Gives a bad taste and slows cooking (pulses and vegetables do not cook well).
- Harms textile, paper and dyeing industries; spoils the texture of clothes and can irritate the skin.
- Hardness is not seriously harmful to health; some studies even suggest that very soft water is linked to heart disease.

Hardness above 500 mg/l as CaCO3 is not acceptable; it is reduced by lime-soda softening or ion exchange.

## Check yourself

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

1. Hardness is caused by dissolved salts of:
   A. calcium and magnesium
   B. sodium and potassium
   C. chlorine and fluorine
   D. iron oxide only
   Answer: A. Also sometimes Fe, Sr, Mn. (Key point: Cause)

2. Temporary hardness is due to bicarbonates and is removed by:
   A. adding chlorides
   B. boiling
   C. filtering
   D. aeration
   Answer: B. Sulphates and chlorides cause permanent hardness. (Key point: Temporary hardness)

3. A main effect of hard water is:
   A. improved lather
   B. faster cooking
   C. scale in boilers and pipes and wasted soap
   D. lower pipe clogging
   Answer: C. Hard water forms scum with soap. (Key point: Effects)

## Related in Water Supply Engineering

- [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
- [Hardness of well water with strontium 25.26 mg/l](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ahardness-bk81) — Water Supply Engineering, chapter 4
- [Living organisms in water; health effects](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aliving-organisms-in-water) — Water Supply Engineering, chapter 4
- [Causes of taste and odour in water](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Ataste-odour-causes) — Water Supply Engineering, chapter 4
- [Typical water supply system and components](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Atypical-ws-system-components) — Water Supply Engineering, chapter 1, asked 4×
- [Protection and maintenance of water supply](https://www.bctengineer.com/question.md?key=semester_5%2Fwater_supply_engineering%3Aws-maintenance-types) — Water Supply Engineering, chapter 7, asked 4×

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