ChemistryChapter 12: Environmental Chemistry — Water
12.2.2 Tap Water
**Tap water** is water supplied through the **municipal water system** to households and for commercial purposes
Explanation level
This topic explains tap water — water supplied through the municipal water system — its sources, treatment, and uses.
Definition
Tap water is water supplied through the municipal water system to households and for commercial purposes.
Simple explanation: Tap water is the water that comes out of your tap at home.
Main Idea
- Streams
- Rivers
- Lakes
- Reservoirs
- Groundwater
It undergoes processes to meet safety standards to make it safe for people.
Simple explanation: Tap water comes from natural sources and is treated to make it safe to drink.
Core Concept
Sources of Tap Water
| Source | Description |
|---|---|
| Streams | Flowing water from rain or snow |
| Rivers | Large natural watercourses |
| Lakes | Large inland bodies of water |
| Reservoirs | Man-made storage for water |
| Groundwater | Water underground in aquifers |
Simple explanation: Tap water comes from rivers, lakes, reservoirs, and underground sources.
Treatment of Tap Water
- Sedimentation
- Coagulation
- Filtration
- Chlorination
- Suspended particles
- Harmful microbes
- Some dissolved impurities
Simple explanation: Tap water is treated to make it safe for people to drink and use.
Detailed Explanation
Where Tap Water Comes From
- Surface water — streams, rivers, lakes, reservoirs.
- Groundwater — water from underground aquifers.
The source depends on the location and availability of water.
Simple explanation: Tap water comes from both surface water and groundwater.
How Tap Water Is Treated
Tap water is treated in a municipal water treatment plant:
- Sedimentation — water stands in a reservoir; suspended matter sinks.
- Coagulation — slaked lime and alum are added; they form a gelatinous mass that traps fine particles.
- Filtration — water is filtered through sand and gravel (sometimes charcoal).
- Chlorination — chlorine is added to kill bacteria.
Simple explanation: Tap water goes through the same four stages as other treated water.
Applications in Chemistry Laboratory
The book gives two main uses of tap water in the lab:
1. General-purpose solvent: - Tap water is used as a solvent for general purposes, such as cleaning glassware, equipment, etc.
2. Educational and simple demonstrations: - It is also used for educational and simple demonstrations as a readily available solvent.
Simple explanation: Tap water is used in labs for cleaning and simple experiments where pure water is not needed.
Tap Water vs Distilled Water
| Feature | Tap Water | Distilled Water |
|---|---|---|
| Source | Municipal water system | Purified by distillation |
| Purity | Contains dissolved minerals and gases | Free of contaminants |
| Electrical conductivity | Higher (due to ions) | Very low |
| pH | Variable (slightly acidic to slightly basic) | 7 (neutral) |
| Uses | Drinking, cleaning, general lab use | Laboratory solutions, calibration |
| Cost | Low | Higher |
Simple explanation: Tap water is treated but not pure; distilled water is highly pure.
Why Tap Water Is Not Used for Precise Lab Work
- Dissolved minerals (Ca, Mg, Na, etc.)
- Dissolved gases (O₂, CO₂)
- Trace impurities
- Interfere with chemical reactions.
- Affect experimental results.
- Contaminate sensitive instruments.
So, for precise lab work, distilled water is used instead.
Simple explanation: Tap water is fine for cleaning, but for precise experiments, distilled water is needed.
Safety of Tap Water
- World Health Organization (WHO) guidelines.
- National drinking water standards.
- Microbial safety (chlorination kills bacteria).
- Chemical safety (limits on toxic substances).
- Acceptable taste, odour, and appearance.
Simple explanation: Tap water is treated to meet safety standards so it is safe to drink.
Intermediate Level
Why Tap Water Is Treated
- Remove suspended particles (sedimentation, coagulation, filtration).
- Kill harmful microbes (chlorination).
- Meet safety standards for drinking water.
- Improve taste, odour, and appearance.
Simple explanation: Treatment makes water safe and pleasant to drink.
Tap Water in the Laboratory
- Cleaning glassware and equipment.
- Rinsing apparatus.
- Simple demonstrations.
- Dissolved minerals can interfere with reactions.
- Dissolved gases can affect results.
- Trace impurities can contaminate samples.
Simple explanation: Tap water is fine for cleaning and simple demos, but not for precise experiments.
Tap Water vs Distilled Water — Detailed
| Feature | Tap Water | Distilled Water |
|---|---|---|
| Source | Municipal supply | Distillation |
| Dissolved minerals | Yes | No |
| Dissolved gases | Yes | Very few |
| Electrical conductivity | Moderate | Very low |
| pH | Variable | 7 |
| Microbial safety | Chlorinated | Sterile |
| Cost | Low | Higher |
| Lab use | Cleaning, simple demos | Precise experiments, calibration |
Safety Standards for Tap Water
- WHO guidelines for drinking water quality.
- National standards for:
- Microbial safety
- Chemical safety
- Radiological safety
- Acceptability (taste, odour, appearance)
Simple explanation: Tap water is tested and treated to meet strict safety standards.
Why Some People Don't Drink Tap Water
- Have an unpleasant taste (due to minerals or chlorine).
- Contain trace contaminants (if treatment is inadequate).
- Be unsafe due to local pollution.
- Bottled water
- Filtered water
- Boiled water
Simple explanation: Tap water is usually safe, but in some areas it may not be ideal for drinking.
Important Points
- - Tap water: water supplied through the municipal water system to households and for commercial purposes.
- - Sources: streams, rivers, lakes, reservoirs, groundwater.
- - Treatment: sedimentation, coagulation, filtration, chlorination.
- - Purpose of treatment: to meet safety standards and make water safe for people.
- - Applications in chemistry laboratory:
- 1. General-purpose solvent (cleaning glassware, equipment).
- 2. Educational and simple demonstrations.
- - Tap water is not used for precise lab work — distilled water is used instead.
Remember
- - Tap water = treated water from the municipal system.
- - Sources: streams, rivers, lakes, reservoirs, groundwater.
- - Treatment: sedimentation, coagulation, filtration, chlorination.
- - Uses in lab: cleaning, simple demonstrations.
- - Not for precise experiments — use distilled water instead.
- - Tap water contains dissolved minerals and gases.
Common Mistakes
- 1. Thinking tap water is pure. Tap water contains dissolved minerals, gases, and trace impurities.
- 2. Thinking tap water is not treated. Tap water is treated (sedimentation, coagulation, filtration, chlorination) to meet safety standards.
- 3. Using tap water for precise experiments. Tap water can interfere with reactions — use distilled water for precise work.
- 4. Confusing tap water with distilled water. Tap water is treated but not pure; distilled water is highly pure.
- 5. Thinking all tap water is the same. Tap water quality varies depending on the source and treatment.
- 6. Thinking tap water is unsafe. In most developed areas, tap water is safe to drink.
Quick Revision
- Tap water: water supplied through the municipal water system to households and for commercial purposes.
- Sources: streams, rivers, lakes, reservoirs, groundwater.
- Treatment: undergoes processes to meet safety standards to make it safe for people.
- Applications in chemistry laboratory:
- Tap water vs distilled water: tap water contains dissolved minerals and gases; distilled water is free of contaminants.
60-Second Revision
- Tap water = treated water from the municipal system.
- Sources: streams, rivers, lakes, reservoirs, groundwater.
- Treatment: sedimentation, coagulation, filtration, chlorination.
- Uses in lab: cleaning, simple demonstrations.
- Warning: tap water is not pure — use distilled water for precise experiments.
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Review the key facts, formulas and checks before you move on.12.2.2 Tap Water
Sticky Notes · Quick Revision
Key Point 1
- Tap water = treated water from the municipal system.
Key Point 2
- Sources: streams, rivers, lakes, reservoirs, groundwater.
Key Point 3
- Treatment: sedimentation, coagulation, filtration, chlorination.
Key Point 4
- Uses in lab: cleaning, simple demonstrations.
Key Point 5
- Not for precise experiments — use distilled water.
Key Point 6
- Tap water contains dissolved minerals and gases.
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