Clean drinking water is essential to life—but the terms used to describe it can be confusing. This glossary explains everything you need to know about drinking water quality, treatment processes, and common contaminants — from TDS and turbidity to reverse osmosis and PFAS.

This guide uses easy-to-understand language to explain common terms, testing, and treatment methods for safe drinking water. For quick answers, feel free to jump to the FAQs below

General Water Quality & Sources

Understanding where our drinking water comes from is the first step to keeping it safe. This section explains basic terms about water sources, how city systems work, and what makes water “safe” to drink. You’ll also learn about the water cycle, wells, and why clear water doesn’t always mean clean water.

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Question 

Answer 

1

What makes water safe to drink?

Safe drinking water has been tested and treated. It is free of harmful germs, metals, and chemicals.

2

What is the difference between “clean” and “safe” water?

“Clean” water looks clear, but it might still have invisible problems. “Safe” water has been tested and meets health rules.

3

Where does most of our drinking water come from?

Most of our water comes from two main places: surface sources (like rivers and lakes) and groundwater (from wells).

4

What is tap water?

Tap water is the water that comes out of your faucet. It’s usually from a city system or a private well.

5

Is rainwater safe to drink?

No, not usually. Rainwater can pick up dust, pollution, and bacteria from the air and roofs, so it needs to be treated first.

6

Can clear water still be unsafe?

Yes. Things like lead, arsenic, or “forever chemicals” can’t be seen, smelled, or tasted.

7

What are water quality standards?

These are the rules set by the government (like the EPA) that say how clean drinking water must be to protect your health.

8

What are the three main steps to make water safe?

The steps are: 1. Cleaning out large stuff (filtration), 2. Killing germs (disinfection), and 3. Testing.

9

How often is city tap water tested?

Water from a public system is tested every day to make sure it is safe for everyone.

10

What is a watershed?

A watershed is the area of land where all the rain and snow drains into one river, lake, or stream.

11

What is groundwater?

Groundwater is water that is stored underground in spaces between rocks and soil. It feeds wells.

12

What is a public water system?

This is the system that treats and delivers safe drinking water to many homes, like in a whole city or town.

13

How does water get from the source to my house?

It goes from the source to a treatment plant, then through a network of underground pipes to your home.

14

What is the water cycle?

It is the natural process where water moves from the Earth to the sky and back again (evaporation, condensation, and rain).

15

What is a “non-community” water system?

This is a system that serves a place like a school, rest stop, or factory, but not a whole town.

16

What is the best type of water to drink?

The best water is water that has been tested, is free of germs and pollutants, and tastes good.

17

Does bottled water come from a special source?

Bottled water often comes from the same source as tap water, but it is usually treated more or differently.

18

How can I get a water quality report for my home?

If you get city water, you can ask your water company for their yearly Consumer Confidence Report (CCR).

19

What is the difference between a river and a reservoir?

A river is natural. A reservoir is a large, man-made lake used to store water for drinking and irrigation.

20

Why is water called the “universal solvent”?

Water can dissolve more substances than almost any other liquid. This is why it can easily pick up pollutants.

Common Contaminants

Not all water problems can be seen, smelled, or tasted. This section covers common contaminants like lead, PFAS, bacteria, and nitrates, explaining where they come from, why they matter, and how they affect your health. You’ll also learn how to spot warning signs such as bad smells or strange colors.

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Question 

Answer 

21

What is lead, and how does it get into drinking water?

Lead is a toxic metal that enters water from old pipes or plumbing. It is very harmful to children.

22

What are Coliform bacteria?

These are a type of bacteria that show there might be harmful germs in the water. It means the water needs to be disinfected.

23

Why does my water smell like rotten eggs?

This is usually caused by hydrogen sulfide gas or sulfur bacteria, often found in well water.

24

What are nitrates?

Nitrates are chemicals from fertilizers, septic tanks, or manure. High levels can be dangerous, especially for babies.

25

What are PFAS chemicals?

They are called “forever chemicals” because they take a very long time to break down. They are found in many household products.

26

How does chlorine get into my tap water?

Water treatment plants add small, safe amounts of chlorine to kill germs and keep the water safe on its way to your house.

27

What causes cloudy or milky water?

The cloudiness is usually tiny, harmless air bubbles. If it clears up after a few seconds, it’s fine.

28

What is arsenic, and why is it dangerous?

Arsenic is a poisonous metal that can be found naturally in the ground. Drinking too much over time can make you very sick.

29

What is a “volatile organic compound” (VOC)?

VOCs are chemicals that easily turn into gas, like paint thinner or fuel. They can get into water from spills or pollution.

30

What is Cryptosporidium?

It is a tiny, tough germ that causes stomach illness. It is a big reason why water must be filtered and disinfected.

31

What causes a metallic taste in my water?

A metallic taste is often caused by copper, iron, or zinc from your home’s plumbing.

32

What are waterborne diseases?

These are illnesses caused by germs (bacteria or viruses) that are spread through unsafe drinking water.

33

What is an emerging contaminant?

This is a new chemical or substance in water that scientists are just starting to study for its possible health effects.

34

Can medicine or drugs get into my drinking water?

Tiny amounts can get in when people flush old medicine. Treatment plants are not always designed to remove them.

35

Why does my water have a strange color, like brown or red?

This often comes from rust (iron) breaking off old pipes, especially when fire hydrants are used nearby.

36

What is algae in drinking water?

Algae are tiny plants in lakes and reservoirs. Some types can release toxins that make water unsafe.

37

What is E. coli?

It is a type of Coliform bacteria that lives in the gut of people and animals. If it’s in your water, it is very unsafe.

38

How can I avoid getting lead in my drinking water?

Always use cold water for drinking and cooking. You can also run your tap for 30 seconds to flush the pipes.

39

What is Giardia?

Like Crypto, Giardia is a germ that causes stomach illness. It’s found in lakes and streams and can pollute water sources.

40

What is the danger of drinking water with a lot of germs?

Germs (like bacteria and viruses) can cause sicknesses like diarrhea, vomiting, and other serious health problems.

Water Treatment & Filtration


Water treatment is what turns raw water into clean, safe drinking water. This section breaks down how different filters and systems work—from simple pitcher filters to advanced methods like reverse osmosis, ion exchange, and UV disinfection. You’ll also learn how cities treat water before it reaches your tap.

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Question 

Answer 

41

What is the main purpose of a water treatment plant?

To remove all harmful things (germs, dirt, chemicals) and make the water safe and good to drink.

42

How does Reverse Osmosis (RO) work?

Water is pushed through a super-fine, special screen (a membrane) that blocks almost all contaminants, like salt and lead.

43

What does activated carbon do in a water filter?

Activated carbon is like a sponge. It has tiny pores that trap chlorine, chemicals, odors, and bad tastes.

44

What is Ion Exchange, and what is it used for?

It is a process that swaps unwanted hard minerals (calcium) with harmless ones (like sodium) to make water soft.

45

What is UV (Ultraviolet) water purification?

A light bulb sends out UV light that zaps and kills germs, viruses, and bacteria without adding any chemicals.

46

How is city tap water disinfected?

Cities often use chlorine, chloramine, or ozone gas to destroy all germs and keep the water safe.

47

What is distillation in water treatment?

Water is boiled until it turns into steam, which leaves all the dirt and minerals behind. The steam is then cooled back into very pure water.

48

What is a whole-house water filter?

It is a large filter system put where the main water line enters your house, so all the water in your home is treated.

49

Do all filters remove fluoride?

No. Only advanced systems like Reverse Osmosis (RO) or special filters can take fluoride out of water.

50

What is a water softener?

A machine that uses the Ion Exchange process to remove the minerals that cause “hard water.”

51

What is a sediment filter?

It’s a basic filter that catches large particles like dirt, rust, and sand before they get to finer filters.

52

What is coagulation and flocculation?

These are treatment steps where chemicals are added to make tiny, invisible particles clump together (coagulate) into bigger, heavier clumps (floc).

53

What is sedimentation?

It is the next step after flocculation, where the heavy clumps (floc) settle to the bottom of a large tank.

54

What is filtration in a treatment plant?

After sedimentation, the water passes through layers of sand, gravel, and charcoal to catch any tiny particles left over.

55

What is oxidation in water treatment?

It is a process that uses oxygen or strong chemicals to change things like iron and manganese so they are easier to filter out.

56

Can I treat my well water at home?

Yes. You can use chlorine, a UV system, or other filters if your well tests show germs or high levels of metals.

57

What is Chloramine?

It is a mix of chlorine and ammonia. Cities use it instead of just chlorine because it stays in the water longer to kill germs.

58

Does a water softener make water safe to drink?

No. It only removes minerals that cause hardness. It does not remove chemicals, germs, or pollution.

59

What is an Aerator?

A device that adds air to the water. This helps remove gases that cause bad smells, like that rotten-egg smell.

60

What is a pitcher filter?

A small, simple filter inside a pitcher that uses activated carbon to quickly improve the taste and smell of water.

61

What is the best filter for removing lead?

Look for a filter that is certified to the NSF Standard 53 or 58. RO systems work best for lead.

62

What does it mean if a filter is point-of-use?

It means the filter only treats the water at one spot, like a faucet or under the kitchen sink.

63

How can I remove chlorine taste from my tap water?

Use an activated carbon filter or simply let the water sit in an open container for a few hours.

64

What is an alternative to chlorine for disinfection?

Ozone (a powerful gas) is often used because it kills germs very quickly and leaves less of a chemical taste.

65

Does boiling water make it safe?

Boiling water for at least one full minute kills all germs and bacteria, but it does not remove lead, nitrates, or chemicals.

Water Quality Terms & Testing

Water testing helps you know what’s really in your tap. This section explains terms like pH, TDS, turbidity, and MCL, so you can read your water report with confidence. It also includes easy tips on how to test your own water and what to do if your test results show problems.

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Question 

Answer 

66

What does pH mean in water?

pH measures how acidic (like lemon juice) or basic (like baking soda) the water is. A number between 6.5 and 8.5 is best.

67

What are Total Dissolved Solids (TDS)?

TDS is the total amount of everything (minerals, salts, metals) that is dissolved and floating in the water.

68

What is turbidity in drinking water?

Turbidity measures how cloudy or murky the water looks. High turbidity is a sign that the water is not filtered well.

69

What is hard water?

Water with a high amount of dissolved minerals, mainly calcium and magnesium. It leaves spots on glasses and scale on pipes.

70

Is hard water bad for your health?

No, hard water is safe to drink and can even give you some helpful minerals, but it is annoying to use with soap.

71

What is a water quality report?

A paper from your water company that lists all the chemicals found in your water and proves it meets all safety rules.

72

What does the EPA’s MCL mean?

MCL means “Maximum Contaminant Level.” It is the highest amount of a specific pollutant allowed in your water.

73

What is conductivity in water?

It measures how well water can carry an electric charge. This is a quick way to check the amount of dissolved minerals (TDS).

74

What does non-detect mean on a water test?

It means the lab tested for that pollutant, but they found an amount so tiny it was too low to measure accurately.

75

How often should I test my well water?

If you have a private well, you should test the water for bacteria, nitrates, and other metals at least once every year.

76

How do I test my tap water at home?

You can buy a simple test kit or send a water sample to a certified lab for a full, accurate check-up.

77

What is Total Organic Carbon (TOC)?

This measures the total amount of carbon found in natural materials (like dead leaves or algae) that are dissolved in water.

78

Can I test for PFAS at home?

No. Testing for chemicals like PFAS requires very expensive and special equipment that only a certified lab has.

79

What is a “boil water advisory”?

A warning issued when the water system may be unsafe. It means you must boil all water before drinking it to kill germs.

80

What should I do if my water fails a safety test?

Stop drinking it immediately. Use bottled water and call your local health department right away.

Regulations, Certifications & Home Use

Knowing who sets water safety rules and how to keep your home system in shape is key to maintaining safe water. This section explains water regulations, filter certifications, and everyday steps to protect your water quality—plus what to do if you notice problems at home.

#

Question 

Answer 

1

What makes water safe to drink?

Safe drinking water has been tested and treated. It is free of harmful germs, metals, and chemicals.

2

What is the difference between “clean” and “safe” water?

“Clean” water looks clear, but it might still have invisible problems. “Safe” water has been tested and meets health rules.

3

Where does most of our drinking water come from?

Most of our water comes from two main places: surface sources (like rivers and lakes) and groundwater (from wells).

4

What is tap water?

Tap water is the water that comes out of your faucet. It’s usually from a city system or a private well.

5

Is rainwater safe to drink?

No, not usually. Rainwater can pick up dust, pollution, and bacteria from the air and roofs, so it needs to be treated first.

6

Can clear water still be unsafe?

Yes. Things like lead, arsenic, or “forever chemicals” can’t be seen, smelled, or tasted.

7

What are water quality standards?

These are the rules set by the government (like the EPA) that say how clean drinking water must be to protect your health.

8

What are the three main steps to make water safe?

The steps are: 1. Cleaning out large stuff (filtration), 2. Killing germs (disinfection), and 3. Testing.

9

How often is city tap water tested?

Water from a public system is tested every day to make sure it is safe for everyone.

10

What is a watershed?

A watershed is the area of land where all the rain and snow drains into one river, lake, or stream.

11

What is groundwater?

Groundwater is water that is stored underground in spaces between rocks and soil. It feeds wells.

12

What is a public water system?

This is the system that treats and delivers safe drinking water to many homes, like in a whole city or town.

13

How does water get from the source to my house?

It goes from the source to a treatment plant, then through a network of underground pipes to your home.

14

What is the water cycle?

It is the natural process where water moves from the Earth to the sky and back again (evaporation, condensation, and rain).

15

What is a “non-community” water system?

This is a system that serves a place like a school, rest stop, or factory, but not a whole town.

16

What is the best type of water to drink?

The best water is water that has been tested, is free of germs and pollutants, and tastes good.

17

Does bottled water come from a special source?

Bottled water often comes from the same source as tap water, but it is usually treated more or differently.

18

How can I get a water quality report for my home?

If you get city water, you can ask your water company for their yearly Consumer Confidence Report (CCR).

19

What is the difference between a river and a reservoir?

A river is natural. A reservoir is a large, man-made lake used to store water for drinking and irrigation.

20

Why is water called the “universal solvent”?

Water can dissolve more substances than almost any other liquid. This is why it can easily pick up pollutants.

Introduction to Drinking Water FAQs

Understanding your drinking water doesn’t have to be complicated. Whether it comes from a city system or a private well, every drop has a story — from its source and treatment to the standards that keep it safe. These quick FAQs cover the most common questions about water quality, contaminants, testing, and home filtration so you can make informed decisions about the water you drink every day.

Safe drinking water has been tested and treated to remove germs, metals, and harmful chemicals. It meets strict health standards set by the U.S. Environmental Protection Agency (EPA).

Most drinking water comes from surface water (like rivers, lakes, and reservoirs) or groundwater (from wells). Public systems treat this water before it reaches your tap.

Yes. Some dangerous contaminants—like lead, arsenic, or PFAS—cannot be seen, smelled, or tasted. Regular testing is the only way to know for sure.

Common contaminants include lead, nitrates, bacteria (like E. coli), chlorine by-products, and PFAS chemicals. Each poses different health risks if not controlled.

City water treatment usually involves filtration, disinfection (with chlorine or ozone), and regular testing to ensure the water meets EPA standards.

Filters certified by NSF International are proven to remove what they claim. Look for NSF 42 (taste/odor), NSF 53 (health-related contaminants like lead), or NSF 58 (reverse osmosis).

Boiling kills bacteria and viruses but does not remove chemicals like lead or nitrates. It’s a good short-term fix for biological contamination only.

Most filters should be changed every 3–6 months. Waiting too long can cause trapped pollutants to release back into the water.

If you ever doubt your water’s safety—test it. Understanding your water’s source, treatment, and quality helps protect your health.

You can request your city’s annual Consumer Confidence Report (CCR) or use a certified lab to test private well water for bacteria, nitrates, and metals.

Family enjoying filtered water together

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