Maharashtra Board Class 4 EVS Chapter 4 Water Safe for Drinking PDF Download

Water Safe For Drinking

Try This

Take a glass half full of water. Add a spoonful of sugar to it and stir it with a spoon.

See what change takes place.

Repeat this experiment with each of the substances mentioned below.

(Wash the glass clean every time you take the next substance.)

Common salt, honey, washing soda, powdered alum, sand, wheat flour, sawdust, turmeric powder and some oil.

What Do You See?

Sugar, salt, washing soda, alum disappear in the water. They dissolve completely in the water. But sand, sawdust, turmeric powder, oil do not disappear even on stirring. They do not dissolve.

What Does This Tell Us?

Some substances dissolve in water, while some substances do not.

The substance that dissolves in water spreads throughout the water. When salt dissolves in water, the water in the container tastes salty. When sugar dissolves, the water tastes sweet.

A New Term!

solution: When a substance dissolves in water, a mixture of that substance and water is formed. This mixture is called the solution of that substance.

If someone gets loose motions, we give them a solution of salt and sugar to drink. This solution is called ORS or oral rehydration solution.

A patient in a hospital is sometimes put on 'saline', that is, on a solution of salt in water. Sometimes, other medicines may also be given through saline.

These are examples of useful solutions.

Teacher's Note

In India, when someone has diarrhea in villages, mothers give ORS solution made from salt and sugar. This helps the body get water back.

Exam Trick

Remember: Solution = solid dissolved in water. Like tea made from tea leaves and hot water. The solid disappears completely.

Points to Remember

Some substances dissolve in water and spread everywhere in it.
Some substances do not dissolve in water at all.
When sugar dissolves, the water tastes sweet.
When salt dissolves, the water tastes salty.
ORS is a solution of salt and sugar used for loose motions.

Do You Know?

Seawater is salty to taste because it is nothing but a solution of salt that occurs naturally. We cannot use seawater for drinking.

Water of different wells may have different tastes. Why is that so? Some substances from the ground dissolve in the water. They give a taste to the well water. But if there is nothing dissolved in water, water has no taste.

When we remove the lid of a soda-water bottle, bubbles fizz out of it. To make soda-water, a gas called carbon dioxide is dissolved in water under pressure. When the lid is removed, the pressure reduces and the gas bubbles out.

Teacher's Note

In India, during monsoon rains, our water becomes salty or tastes different because of minerals dissolved in it. This is normal.

Exam Trick

Remember: Soda water bubbles are CO2 gas coming out. When you open the bottle cap, gas escapes because pressure is released.

Points to Remember

Seawater is salty because salt is dissolved in it naturally.
Different wells have different water tastes because of dissolved minerals.
Pure water has no taste, color, or smell.
Carbon dioxide gas is dissolved in soda water under pressure.
When pressure reduces, gas bubbles come out.

Try This

Fill a large container with water.

Collect the following articles.

From your compass box: a plastic ruler, an eraser, a pencil, a sharpener, a rubber band, the compass.

From your house: a steel spoon, a plastic spoon, some groundnut shells, an iron nail, a screw, a coin.

From outdoors: stones, little twigs, leaves, soil.

Put these things in the water and see whether each of them sinks or floats.

What Do You See?

The eraser, sharpener, steel spoon, nail, screw, stones, coin, the compass and the soil sink in the water while the other things float.

What Does This Tell Us?

Some things float on water while some things sink in it.

The things that float are lighter than water. The things that sink are heavier than water.

Teacher's Note

In India, wooden toys and plastic toys float in water because they are light. Iron things sink because they are heavy.

Exam Trick

Remember: Light things float, heavy things sink. Like a rubber ball floats but a stone sinks.

Points to Remember

Things lighter than water float on it.
Things heavier than water sink to the bottom.
Plastic floats but steel sinks.
An eraser sinks but rubber floats.
We can separate things by using their float and sink properties.

Try This

Take some muddy water in a big beaker. (If you do not find muddy water, then make some by adding some soil, pieces of dry twigs, straw, leaves, etc. to water.)

Now allow this beaker to stand still for four or five hours.

What Do You See?

The particles of soil sink in the water and form a layer or sediment at the bottom. But twigs and other rubbish float on the water. It takes a long time for the sediment to form.

What Does This Tell Us?

Particles of soil are heavier than water. But because they are very small, they take a long time to settle to the bottom of the water. Leaves, twigs, etc. are lighter than water.

Now the water appears much cleaner and transparent than it was.

The process of allowing heavier particles to settle to the bottom of still water is called 'settling'.

Without disturbing the sediment, pour the water above it into two smaller beakers. Even though this water appears much cleaner than before, there are still some fine particles of soil and some rubbish floating in it.

Now carry out the following experiments using these two beakers. Label them 1 and 2.

Try This

Take a piece of alum and swirl it once in the water in the first beaker.

Leave this beaker undisturbed for two or three hours.

What Do You See?

The particles floating in water slowly settle to the bottom. And the water in the upper part becomes transparent. The twigs and straw still keep floating on the water.

What Does This Tell Us?

Swirling alum in water helps the soil particles in muddy water to settle down.

After doing this experiment, throw the water into the soil and wash your hands with soap and clean water.

Teacher's Note

In Indian villages, people use alum powder to clean muddy water. Alum helps dirt particles stick together and sink quickly.

Exam Trick

Remember: Alum powder clears muddy water. Just add a little alum and wait. The mud will settle down quickly.

Points to Remember

Settling is when heavy particles go to the bottom of water.
Alum powder helps clean muddy water faster.
Sediment is the layer of dirt at the bottom.
After settling, water looks cleaner but may not be safe to drink.
Twigs and leaves float because they are light.

Try This

Take another beaker. Place a tea strainer over it. Fold a piece of fine cotton cloth into four layers. Make it moist and spread it over the strainer. Now pour the water in beaker 2 in a thin stream on the folds of the cloth.

What Will You See?

The rubbish and soil particles remain on the cloth.

The water collects in the beaker below. It looks transparent.

What Does This Tell Us?

If we strain muddy water, it helps to make it clean. This process is called filtration.

After doing this experiment, throw the water into the soil and wash your hands with soap and clean water.

A New Term!

potable water (water safe for drinking): Water that does not endanger our health in any way when we drink it is called safe drinking water or potable water.

We have seen some methods of making muddy water clean and transparent. However, such water may still not be potable.

Can You Tell?

In the rainy season, the water of rivers and streams becomes muddy. Why do we not drink that water?

When on an excursion, if you find that the water of a spring or well there has a bad smell, would you drink it?

Teacher's Note

In India, during monsoon, river water becomes muddy. But even after settling and filtering, it may have harmful germs. We must boil it to drink safely.

Exam Trick

Remember: Clean water ≠ Safe water. Always boil water before drinking during rainy season.

Points to Remember

Filtration removes visible dirt from water.
Potable water is safe to drink without causing illness.
Clear water may still contain harmful micro-organisms.
Boiling water kills germs and makes it safe.
Water with bad smell or color should never be drunk.

This is a preview of the first 3 pages. To get the complete book, click below.