How is water made safe to drink?

How is water purified?

Water purification can be done using several methods, depending on the type of contaminants (microorganisms, chemicals, sediments, heavy metals, etc.). They range from the very simple (boiling) to the very high-tech (Ozonation or EDI). Here are the main methods:

1. Physical Methods

Boiling

Kills most pathogens (bacteria, viruses, protozoa). Simple and effective but doesn’t remove chemical contaminants.

• Pros:
  - Very effective at killing bacteria, viruses, and protozoa.
  - Simple, requires no special equipment
• Cons:
  - Doesn’t remove chemicals, salts, or heavy metals.
  - Requires fuel/energy (not ideal for large-scale use).
  - Water may taste flat after boiling.

Filtration

Uses physical barriers to remove suspended solids, sediments, and some microorganisms. Common filters include ceramic, sand, and ultrafiltration membrane filters.

• Pros:
  - Removes sediments, dirt, and many pathogens.
  - Portable options available (e.g., ceramic filters).
  - Improves taste and clarity of water.
• Cons:
  - Doesn’t always remove viruses or dissolved chemicals.
  - Filters clog and need cleaning/replacement.

Sedimentation

Letting water sit so heavier particles settle to the bottom. Used in waste water treatment.

• Pros:
  - Very simple, no energy needed.
  - Useful as a pre-treatment before other methods.
• Cons:
  - Only removes heavy particles, not microbes or chemicals.
  - Takes time to be effective.

Distillation:

Heating water to produce steam and condensing it back to liquid. Removes salts, heavy metals, and microbes but is energy-intensive.

• Pros:
  - Removes microbes, salts, and heavy metals.
  - Produces very pure water.
• Cons:
  - Energy-intensive and slow.
  - Can remove beneficial minerals, making water taste flat.
  - Not practical for large-scale or emergency use.

2. Chemical Methods

Chlorination

Adding chlorine or chlorine compounds kills most bacteria and viruses. Common in municipal water treatment.

• Pros:
  - Kills bacteria and viruses effectively.
  - Inexpensive, widely used in municipal systems.
  - Residual chlorine protects water during storage.
• Cons:
  - Less effective against protozoa (e.g., Giardia, Cryptosporidium).
  - Can produce harmful by-products (trihalomethanes).
  - Some people dislike chlorine taste/odour.

Ozonation:

Using ozone gas to disinfect water. More powerful than chlorine, leaves no taste, but requires special equipment.

• Pros:
  - More powerful disinfectant than chlorine.
  - Doesn’t leave taste or odour.
  - Effective against bacteria, viruses, and protozoa.
• Cons:
  - Expensive equipment.
  - No residual effect (water can get recontaminated).

Iodine Treatment:

Often used in emergency kits for small amounts of water.

• Pros:
  - Portable, useful in emergencies.
  - Kills bacteria and viruses effectively.
• Cons:
  - Unpleasant taste and odour.
  - Not suitable for long-term use (can affect thyroid health). 
  - Less effective against some protozoa.

Chemical Coagulation and Flocculation:

Adding chemicals (like alum) to bind suspended particles into larger clumps that settle or can be filtered out.

• Pros:
  - Removes turbidity, suspended solids, and some microbes.
  - Commonly used in large-scale water treatment.
• Cons:
  - Requires chemicals (alum, ferric salts).
  - Needs proper handling and equipment.
  - Doesn’t kill microbes directly (needs disinfection step).

3. Biological Methods

Slow Sand Filtration:

Uses a biological layer (schmutzdecke) formed on sand that removes pathogens and organic material.

• Pros:
  - Natural, low-cost, sustainable.
  - Removes pathogens and organic matter.
  - Long-lasting with proper maintenance.
• Cons:
  - Requires space and regular cleaning.
  - Works slowly, not ideal for emergencies.
  - Doesn’t remove chemicals.

Biochar Filtration:

Uses carbon-based filters to remove microbes and toxins.

4. Membrane Technologies

Reverse Osmosis (RO):

Forces water through a semi-permeable membrane to remove salts, heavy metals, and microbes. Common in household purifiers.

• Pros:
  - Removes salts, heavy metals, microbes, and many chemicals.
  - Provides very pure water.
• Cons:
  - Expensive (equipment and maintenance).
  - Wastes water (2–3 litres wasted per litre purified).
  - Strips beneficial minerals from water

Ultrafiltration (UF):

Removes bacteria, protozoa, and viruses - depending on the pore size - but allows dissolved salts and small molecules to pass.

• Pros:
  - Removes bacteria, protozoa, and some viruses.
  - No electricity required.
• Cons:
  - Doesn’t remove dissolved salts or chemicals.
  - Filter replacement needed.

Nanofiltration:

Removes divalent salts, organic molecules, and some viruses. Used in waste water treatment by water suppliers.

• Pros:
  - Removes bacteria, protozoa, viruses, pesticides and some salts.
  - Produces softer water.
  - Energy efficient
• Cons:
  - Doesn’t remove

5. Advanced/Modern Methods

Ultraviolet (UV) Irradiation:

Exposes water to UV light to kill microbiological contaminants. Doesn’t remove chemicals.

• Pros:
  - Very effective at inactivating microbes (bacteria, viruses, protozoa).
  - No chemicals, no change in taste.
  - Fast and easy.
• Cons:
  - Needs electricity.
  - Doesn’t remove chemicals or turbidity.
  - Water must be clear for UV to work properly.

Activated Carbon Filtration:

Adsorbs organic compounds, chlorine, pesticides, odours, and unpleasant tastes.

• Pros:
  - Removes chlorine, pesticides, organic compounds, odours.
  - Improves taste significantly.
  - Often combined with other methods.
• Cons:
  - Doesn’t kill microbes.
  - Requires replacement when saturated.

Electrodeionization (EDI):

Uses electricity and ion-exchange membranes to remove ionized species, used to produce high-purity water for pharmaceuticals and electronics applications.

• Pros:
  - Sustainable alternative to chemical deionization
  - Continuous process
• Cons:
  - Uses electricity
  - Expensive, specialised process

Solar Disinfection (SODIS):

Exposing water in clear plastic bottles to sunlight (UV + heat) for several hours.

• Pros:
  - Very low-cost, uses only sunlight and plastic bottles.
  - Effective against most microbes.
  - Useful in remote/low-resource areas.
• Cons:
  - Requires clear plastic bottles and full sun.
  - Takes several hours.
  - Doesn’t remove chemicals or sediments.

Graphene:

The new kid on the block, graphene filtration has the potential to provide the cleanest, safest water possible, proving effective at reducing PFAS/PFOA (forever chemicals), heavy metals, antibiotics, chemicals and more. This new adsorption technology is till very new so water companies are still working out the best way of utilising it. LifeSaver is about to launch a graphene-enhanced filter for the Jerrycan; for the first time, travellers will have the option of extra protection when in particularly hazardous locations.

• Pros:
  - The only filtration method shown to tackle PFAS.
  - Works alongside ultrafiltration.
• Cons:
  - Expensive
  - Still in it's infancy

Summary

The water treatment plants that supply tap water usually combine several methods (e.g., coagulation, sedimentation, filtration, and disinfection) to ensure it's safe to drink. Whether the water tastes good will depend on the methods used and the level of contaminants it originally contained. Some contaminants may taste unpleasant or cause chaos in your kettle, but they aren't actually harmful so, even with the best purification methods used, the resulting water can disappoint. 

When it comes to portable water purifiers, some of these methods work can really well when on the road, others simply aren't an option. When choosing a purifier for your next trip it's important that you do your research. In some parts of the world the municipal systems in place aren't always reliable and, in the event of flooding or pipe damage, even the most sophisticated water suppliers can let you down. (Keeping a portable water purifier for use in an emergency is always a good idea.) Know what water challenges you are likely to face and check that the purifier you choose is up to the task. 

If you'd like help or advice please don't hesitate to get in touch.