NCWR

About NCWR

Desalination

In a nutshell

In this activity we visit a desalination plat and learn about what it takes to convert salt water to fresh one.

A school day

12-13 years old

In the field

Our objectives

In this activity you will:

  • Find out how sea and brackish water can become freshwater
  • Be informed about the uses of desalinated water

Things to use

Notebooks and pens, shallow glass or plastic dish (petri dish), photo camera (or cell phone to take photos)

Play & learn

Salt vs. fresh water

Do you know the percentage of the Earth’s surface that is covered by water?


Use of salt water

Why don’t we use these huge amounts of water to tackle the water shortages that some places in the world are facing?


Stop and wonder

Did you know that?


  • Salt in water is a result of the rocks being eroded and dissolved in water for millions of years.
  • The rivers carry about 4 billion of tons of salt every year at sea.
  • Salinity[/glossary] of water depends on the location? It is higher in tropical areas (due to intense evaporation) and lower in the poles due to ice melting and rainfalls; it is relatively low near the continents due to freshwater springs.
  • The Mediterranean is considered a rather “salty sea” with high salinity.
  • Although desalination is an energy and cost demanding technology, it provides a reliable supply of water regardless of the weather conditions or season (i.e. during high demand tourist/summer seasons) for water scarce areas.
  • The Mediterranean region holds about 17% of global seawater desalination capacity.
  • Desalinated water can supplement municipal water supplies and it is used also in industry and .

 

Activity

From salt to fresh water

  1. Collect about 100 mL of seawater or brackish water.
  2. Add a small quantity of this water to a Petri dish (see the image) or any shallow glass container. Make sure that the dish is clear!
  3. Place the dish in a sunny spot for  2-3 days to let water evaporate.
  4. What do you observe on the dish ?

Water-readings

Reverse Osmosis

The basic steps followed in a Reverse Osmosis (desalination) unit to produce freshwater from sea (or brakish) water are the following:

  1. Intake: Seawater is transferred to the plant through pipes, and thus the units are built near the coast.
  2. Pre-treatment: During pre-treatment water is filtered to remove debris, floating particles, etc.
  3. Salt removal process: The saltwater passes through a series of semi-permeable membranes with high pressure, and due to “reverse osmosis” the salts are retained on the membranes.
  4. Post-treatment: Desalinated water is further treated to avoid infection by microorganisms (disinfection) and to improve its taste. In some cases, it is mixed with freshwater (groundwater).
  5. The desalinated water enters the water supply network. Usually, the volume of the desalinated water is about half the initial (intake) volume.
  6. The remaining water of high salinity /brine is discharged back to the sea. Before that it operates (turns) an energy turbine, and this way, it reclaims some of the energy consumed in the desalination unit.

Play & learn

Based on what you read so far, identify the steps followed in a desalination plant (drag and drop them to the right spot).

 desalination quiz-hotspot
1
2
3
4
5
6
7
8
  • 1 1 intake pipes
  • 2 2 outtake pipes/discharge of brine
  • 3 3 pre-treatment
  • 4 4 reverse osmosis membranes
  • 5 5 distribution network
  • 6 6 post-treatment
  • 7 7 energy turbine
  • 8 8 energy station

Group activity

Visiting a desalination plant

Organise a visit to a desalination plant to collect information  about the processes followed.

Before your visit


  • Observe on the map the area where the plant is located. Why do you think the particular area was chosen?

During your visit


  • Keep notes and take photos of all steps/processes.
  • Ask the staff what they do with the resulting brine.
  • Ask the staff what is main energy resource used for the plant’s function.
  • Ask the staff what if the plant applies any measures to reduce its climate footprint.

Play & learn

What could be the alternatives to the negative aspects of desalination? Drag and drop!

A: Negative aspects

B: Alternatives / Remedies

  • 1 If the energy required to run the unit derives from fossil fuels, the unit generates a considerable amount of CO2 emission 1
  • 2 The intake and discharge of the residue brine may have impacts on marine biodiversity. 2
  • 3 The desalination unit has a high cost of installation and function. 3
  • 1 The unit can be linked with renewable energy resources (e.g. solar, wind).
  • 2 Proper planning and management is needed on both points of intake and brine discharge.
  • 3 Ensuring a reliable water supply in dry areas (e.g. in areas where no other options exist) enhances the economic and social development of the area.

Water meter

I liked this activity . . .

Way forward

Dive in…

Rainwater harvesting Do you know about grey water? Wastewater treatment

if you want to know about other non-conventional water resources.

or go back to the homepage!

Water works through time

Water in the city

The water basins

Desalination

Greywater recycling in practice

Do you know about grey water?

Wastewater treatment

Rainwater Harvesting Systems in practice

Rainwater harvesting

Reduce-Reuse-Recycle

Acting for Climate

Climate change: Why should I care?

Water resources

The water cycle

Where do I begin?

Water works through time

Let's discover the story behind the old fountains, cisterns and aqueducts of our town!

Continue!

Water in the city

What is the "urban water cycle"? Which are the important aspects of water management within a city environment?

Continue!

The water basins

In this activity we learn what a water drainage basin is and why it is important for the experts to study it.

Continue!

Desalination

Let's find out how sea and brackish water can become a freshwater resource!

Continue!

Greywater recycling in practice

How a greywater system is installed? Let's find out!

Continue!

Do you know about grey water?

Let's find out what "greywater” is and how we can use it!

Continue!

Wastewater treatment

In this activity we learn about how wastewater is treated and what we can do with the treated water.

Continue!

Rainwater Harvesting Systems in practice

What are the various types of rainwater harvesting systems? Let's find out more about them!

Continue!

Rainwater harvesting

Can we collect rainwater? And how do we use it? Let's find out!

Continue!

Reduce-Reuse-Recycle

What is our water footprint and how can we reduce it?

Continue!

Acting for Climate

What are the main sectors contributing to climate change? What are countries doing to address it? What can we do for climate collectively at school and at community level?

Continue!

Climate change: Why should I care?

We discuss the greenhouse effect and the greenhouse gases, how climate change is linked to our lifestyles and ways we can cope with it on a personal level.

Continue!

Water resources

Lt's discover the water resources of our region.

Continue!

The water cycle

Let's travel within the water cycle!

Continue!

Where do I begin?

Let's see why it is important to know about water in our region.

Continue!