Drinking Water

Question 1

Why do we need clean water?

Answer 1

To protect human health, prevent diseases, and ensure safe, pleasant, and non-toxic water for drinking and use.

Question 2

What are the two main categories of impurities in water?

Answer 2

Undissolved matter and dissolved matter.

Question 3

Examples of undissolved matter in water?

Answer 3

Organic: decayed plants/waste. Mineral: sand, silt, clay. Also microorganisms like bacteria and protozoa.

Question 4

How do we measure undissolved matter?

Answer 4

By turbidity (NTU), suspended solids (mg/L), and particle count (per size).

Question 5

Examples of dissolved macropollutants (>1 mg/L)?

Answer 5

Natural organic matter, O2, CO2, NaCl, CaCO3, Fe, Mn, NH3, CH4, H2S.

Question 6

Examples of dissolved micropollutants (<1 mg/L)?

Answer 6

Pesticides, pharmaceuticals, PFAS, heavy metals (Pb, Cd, As), radioactive compounds.

Question 7

What does COD measure?

Answer 7

Chemical Oxygen Demand measures oxygen required to chemically oxidize organic matter with K2Cr2O7.

Question 8

What does BOD measure?

Answer 8

Biochemical Oxygen Demand measures oxygen consumed by microorganisms to degrade organic matter.

Question 9

What does TOC stand for and measure?

Answer 9

Total Organic Carbon; measures total carbon content of organic matter in water.

Question 10

Why is color measured in drinking water analysis?

Answer 10

To detect humic acids or dissolved organics, compared using Pt/Co standard solution.

Question 11

Give examples of pathogenic microorganisms in water.

Answer 11

Bacteria (E. coli, Salmonella), viruses (Rotavirus), protozoa (Giardia), helminths (Dracunculus).

Question 12

Name common indicator organisms in water testing.

Answer 12

E. coli, total coliforms, enterococci, Clostridium perfringens, coliphages, HPC.

Question 13

What physical parameters are checked in drinking water?

Answer 13

Temperature, turbidity, color, and odor.

Question 14

What are typical limits for E. coli in drinking water?

Answer 14

0 per 100 mL (NL, EU, WHO).

Question 15

What are trihalomethanes (THMs)?

Answer 15

By-products formed when chlorine reacts with natural organic matter during disinfection.

Question 16

List the main sources of drinking water.

Answer 16

Groundwater, surface water, rainwater, seawater, water vapor, and treated wastewater.

Question 17

Advantages of groundwater as a source?

Answer 17

Naturally filtered, constant quality, usually safe with minimal treatment.

Question 18

Disadvantages of groundwater as a source?

Answer 18

Over-extraction causes depletion; saltwater intrusion in coastal zones.

Question 19

Main issues found in groundwater?

Answer 19

Fe2+, Mn2+, CH4, H2S, CO2, and sometimes As, B, F.

Question 20

Purpose of aeration in groundwater treatment?

Answer 20

To oxidize Fe2+, Mn2+, NH4+ and remove dissolved gases like CH4, CO2, H2S.

Question 21

Give the chemical equation for iron oxidation during aeration.

Answer 21

4Fe2+ + O2 + 10H2O → 4Fe(OH)3(s) + 8H+.

Question 22

Main types of aerators?

Answer 22

Cascade, spray nozzle, air diffusion, and tower aerators.

Question 23

Which aeration method best removes CO2?

Answer 23

Tower aeration.

Question 24

Which aeration methods best remove CH4?

Answer 24

Spraying and tower aeration.

Question 25

Purpose of rapid sand filtration?

Answer 25

To remove oxidized metals (Fe, Mn) and support biological nitrification (NH4+ → NO3-).

Question 26

What is backwashing in filtration?

Answer 26

Reversing water flow to clean clogged filters and remove accumulated solids.

Question 27

Advantages of surface water sources?

Answer 27

Abundant and easy to collect.

Question 28

Disadvantages of surface water sources?

Answer 28

High contamination risk, seasonal changes, and need for complex treatment.

Question 29

Main steps in conventional surface water treatment?

Answer 29

Reservoir → Coagulation/flocculation → Sedimentation → Sand filter → Activated carbon → Disinfection.

Question 30

Purpose of coagulation in treatment?

Answer 30

Neutralize particle charges so colloids can stick together.

Question 31

Purpose of flocculation in treatment?

Answer 31

Gentle mixing to form larger flocs that can settle easily.

Question 32

Why is a jar test used?

Answer 32

To find the optimal coagulant dose and mixing time for effective floc formation.

Question 33

Function of activated carbon filters?

Answer 33

Adsorb small organic compounds, remove odor, taste, and micropollutants.

Question 34

Difference between GAC and PAC?

Answer 34

GAC = granular and reusable; PAC = powdered and single-use.

Question 35

Principle of membrane processes?

Answer 35

Separation based on particle size (MF < UF < NF < RO).

Question 36

Main drawback of membrane processes?

Answer 36

Handling the concentrated reject stream containing all contaminants.

Question 37

Goal of disinfection in drinking water?

Answer 37

Eliminate remaining microbes and prevent regrowth in distribution pipes.

Question 38

Compare UV vs Chlorination.

Answer 38

UV: no chemicals, no by-products, no residual. Chlorination: chemical, leaves residual, can form THMs.

Question 39

What is the average daily water use per person in the Netherlands (2022)?

Answer 39

About 128 liters per day.

Question 40

Target water use per person in the Netherlands by 2035?

Answer 40

100 liters per day.

Question 41

Main household water uses in NL?

Answer 41

Showering, toilet flushing, laundry, hand washing.

Question 42

How can water use be reduced?

Answer 42

Vacuum toilets, greywater reuse, public awareness.

Question 43

Steps in Pureit™ household water purifier?

Answer 43

1. Microfiber mesh, 2. Carbon trap, 3. Germkill chlorine unit, 4. Polisher.