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 amd brakish water can become freshwater
  • Explore 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?


  1. Salt in water is a result of the rocks being eroded and dissolved in water for millions of years?
  2. The rivers carry about 4 billion of tons of salt every year at sea?

The composition of seawater is quite complex  and salts can be found in a wide range of quantities (concetration).   depends on the location: it is higher in tropical areas, because of intense evaporation due to winds and high temperatures; it is lower in the poles due to ice melting and rainfalls; it is relativly low also near the continents due to freshwater springs. The Mediterranean is considered a rather “salty sea” with high salinity.

Desalination refers to the process of removal of salts and other minerals from salt and water to produce fresh water.  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 .

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).

Group 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 or 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

There are two main methods that are used to produce desalinated water, distillation and Reverse Osmosis (RO) process.

Reverse Osmosis

The basic steps followed in a RO plant, 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.
  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 including the 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 salty 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 generated 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

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Way forward

Dive in…

Rainwater harvesting Do you know about grey water? Wastewater treatment

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

or go back to the homepage!

The water basins

Water in the city

Desalination

Do you know about grey water?

Rainwater harvesting

Greywater recycling in practice

Wastewater treatment

The water cycle in a bowl!

Waterworks through time

Climate change challenges

Rainwater Harvesting Systems in practice

Reduce-Reuse-Recycle

Water resources

Where do I begin?

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!

Water in the city

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

Continue!

Desalination

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

Continue!

Do you know about grey water?

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

Continue!

Rainwater harvesting

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

Continue!

Greywater recycling in practice

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

Continue!

Wastewater treatment

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

Continue!

The water cycle in a bowl!

Let's travel within the water cycle!

Continue!

Waterworks through time

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

Continue!

Climate change challenges

Time to discuss about climate change, causes and impact and how we can cope with it.

Continue!

Rainwater Harvesting Systems in practice

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

Continue!

Reduce-Reuse-Recycle

What is my water footprint and how can I reduce it?

Continue!

Water resources

Discovering the water resources of our region.

Continue!

Where do I begin?

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

Continue!