1 Mark Questions
Question 1 : What is potable water?
Answer : Water which is free from impurities and is safe for human consumption is known as potable water.
Question 2 : Mention two qualities of drinking water.
Answer : The two qualities of drinking water are:
(i) It should be clear, odourless and have a good taste.
(ii) It should be free from all undesirable chemical substances.
Question 3 : State two reasons why the drinking water which looks clear is unsafe?
Answer : Drinking water which looks clear may be unsafe because:
(i) It may have objectionable taste.
(ii) It may also have harmful bacteria in it.
Question 4 : Mention some household uses of water.
Answer : Water is one of the basic necessities of any household. It is required for any personal cleaning like bathing, washing clothes, cleaning utensils, cooking food and household cleaning as well as for drinking.
Question 5 : What is impure water?
Answer : Impure water is one which is not safe for drinking. Water can be impure because of physical impurities caused by mixing of certain substance or it can be due to presence of harmful bacterias in it.
2 Marks Questions
Question 6 : Inspite of boiling, the drinking water was declared unsafe, what could be the four possible reasons for this.
or
“Use of boiling method may not always assure you to get safe potable water.” Support this statement with four reasons.
Answer : Boiling water is one of the common method of making water safe for drinking. But still due to some reasons we may not always get safe potable water by boiling. The reasons can be:
(i) The boiling is done for less than the minimum to 10 minutes required.
(ii) The container used for boiling the water is not properly cleaned.
(iii) The water has not been strained before boiling, so that some suspended matter remains in it.
(iv) It may still contain pesticides, insecticides and herbicides, as these are not eliminated by boiling.
Question 7 : Use of chlorine tablets may not always assure you to get safe potable water. Support this statement with four reasons.
Answer : Most of the time chlorine tablets may assure us to get safe potable water. But sometimes even chlorine tablets may not be able to assure us safe potable water because:
(i) The chlorine tablets used were old and past their expiry date.
(ii) The tablets had been stored in an open container prior to use and so were ineffective.
(iii) The number of tablets used were much less than the prescribed quantity.
(iv) The water container was not sealed for a minimum time of 10 minutes for the chlorine tablets to take effect.
3 Marks Questions
Question 8 : For purifying her drinking water, Geeta has to buy either reverse osmosis filter or an ordinary electric filter. Help her to take a decision by giving her the necessary information. Help her to take a decision by giving her the necessary information she should required about require about these filters.
Answer : The necessary information about electric filter and reverse osmosis filter is given in the table below. According to her budget, she can make a decision and buy either filter.
| Electric Filter | Reverse Osmosis Filter |
| It has a candle which takes care of suspended particles. | It has a sediment filter which removes suspended particles. |
| Carbon granules remove chemical impurities. | There are two activated carbon filters which remove chemicals and enhance taste. |
| It is cheaper. | It is expensive. |
| Filter has to be changed every six months. | Filter needs to be changed once in a year. |
| No wastage of water. | About 50% water is wasted. |
| Ultraviolet light kills germs and micro-organisms. | Semi-permeable membrane removes lead, arsenic, etc. |
If her budget allows, Geeta should go for a RO system as it will be a good investment for the long run.
Question 9 : For purifying her drinking water, Geeta has been using chlorine tablets. Now, she wants to buy a reverse osmosis filter. Compare the advantages and drawbacks of both theses methods and state whether her decision is right or not.
Answer : Geeta must look at the table given below and compare the two systems. Though RO system is a bit expensive but Geeta is right in buying this as it is the most effective method of purifying water and it lasts for a long time.
| Chlorine Tablets | Reverse Osmosis |
| Cheap | Expensive. |
| Very useful while travelling. | Cannot be taken outside the house. |
| No wastage of water. | About 50% water is wasted. |
| Suspended particles are not removed. | All impurities are removed. |
| Water contains smell of chlorine. | No smell. |
| Taste is a little bitter. | Tasteless. |
| Effective. | Effective. |
Question 10 : Write two advantages and two drawbacks of using chlorine tablets for making water potable. Why is it more popular than boiling method?
Answer : Two advantages of using chlorine tablets for making water potable are:
(i) It is a cheap, simple and convenient method to purify water.
(ii) These tablets are able to kill all bacterial contaminants present in the water.
Two drawbacks of using chlorine tablets for making water potable are:
(i) Excessive use of chlorine harms our health.
(ii) Sometimes, water gives a smell of chlorine and gives a bad taste.
Inspite of disadvantages, use of chlorine tablets is more popular than boiling method because boiling requires a lot of fuel (i.e. it is costly). Time consuming and inconvenient for a large family.
| Boiling Method | Chlorine |
| It is an expensive method as it requires a lot of fuel. | It is very cheap method. |
| It is very time consuming method. | It is not at all time consuming. |
| Not convenient for a large family. | Can be used very easily in large gatherings, for e.g. Military camps. |
Question 11 : People of Basra village use alum to make their water potable. Convince them to use chlorine instead. Tell them about the procedure to use these tablets and two precautions while using them.
Answer : Use of chlorine tablets to make water potable is cheaper and more effective than the use of alum, because alum does not kill coliform bacteria. The procedure to clean water with the help of chlorine tablets is :
(i) Dissolve one tablet in 10 litres of water.
(ii) Leave for 10 minutes before consuming.
(iii) Filter the water and use it.
Advantages of this method are:
(i) It is convenient to use.
(ii) It is very cheap.
(iii) It kills coliform bacteria.
Precautions to be taken are:
(i) Use the tablets before their expiry date.
(ii) Keep tablets at a dry place.
(iii) If water is very dirt, use more tablets and wait for 20 minutes before using the water.
Question 12 : People of Basra village use four pitcher filters to purify their water. Convince them to use chlorine tablets instead. Also tell them the necessary procedure for using the tablets and precautions to be taken while using them.
Answer : Refer to Q. No. 11.
Question 13 : The potable water that looked clear was declared unsafe by the authorities. State any two reasons for this. How will you make this water safe using boiling method?
Answer : The possible reasons due to which the water was declared unsafe by the authorities may be:
(i) It had an unacceptable amount of coliform bacteria in it.
(ii) It had dissolved gaseous and other harmful impurities in it.
We can make this water safe by using the boiling method as follows:
(i) Keep the water in a clean container until any suspended solids settle at the bottom.
(ii) The top water is then strained and boiled for 10 minutes.
(iii) The water is cooled and kept in clean container for use.
Question 14 : The potable water that looked clear was declared unsafe by the authorities. State any two reasons for this. How will you educate the public to use chlorine tablets and take necessary precautions for making this water potable?
Answer : For reasons due to which the water declared unsafe by the authorities, refer to Q. No. 13.
People should use chlorine tablets for purifying the water because:
(i) It is safe and effective method as all bacterial contaminants are killed.
(ii) It is the cheapest, simple, effective and the most reliable method to disinfect water.
(iii) It can be used to purify large quantities of water.
Necessary precautions to be taken while using chlorine tablets for making this water potable are:
(i) The chlorine tablets should be used before their expiry date.
(ii) The tablets should be stored in a dry closed container prior to use.
(iii) They should be used only in the prescribed quantity, as excess quantity can be harmful.
Question 15 : The potable water that looked clear was declared unsafe by the authorities. State any two reasons for this. How will you educate the public to use alum for making this water potable?
Answer : For reasons due to which the water declared unsafe by the authorities, refer to Q. No. 13.
People should use alum for purifying the water because:
(i) It removes all suspended impurities through coagulation, which then sink to the bottom and the water can then be strained.
(ii) Alum has disinfection properties, killing the bacteria in the water.
Question 16 : Write four benefits of using an Electric water filter. List two specific precautions you would adopt if you are using such a filter for potable water.
Answer : An electric water filter has the following benefits:
(i) It provides safe, cool and potable water.
(ii) It saves gas consumption.
(iii) Large quantity of water can be made potable in a short time.
(iv) It kills bacteria and viruses.
Some precautions while using electric filter are:
(i) The water supply should be continuous.
(ii) Only water at room temperature should be passed through the filter.
Question 17 : Describe the easiest method of purifying water while travelling by train. Give two benefits and two drawbacks of the procedure used.
Answer : The easiest method of purifying water during travelling is use of chlorine tablets. These tablets are easily available at any chemist’s shop. For benefits and drawbacks of using chlorine tablets, refer to Q. No. 10.
Question 18 : Name any two diseases caused by drinking polluted water. Give two precautions each you would adopt while using electric filter and chlorine tablets to make this water potable.
Answer : Two diseases caused by drinking polluted water are cholera, diarrhoea, etc.
Precautions to adopt while using electric filter are:
(i) The water to be filtered should be at room temperature. Hot water will damage the candle.
(ii) The candle must be changed at regular intervals.
Precautions to adopt while using chlorine tablets are:
(i) The chlorine tablets should be stored in a dry closed container prior to use.
Question 19 : Name any two diseases caused by drinking polluted water. Give two precautions each you would adopt while using Alum and chlorine tablets to make this water potable?
Answer : Two diseases caused by drinking polluted water are cholera, diarrhoea, etc.
Precautions to adopt while using alum are:
(i) Use the alum in appropriate proportion to the quantity of water.
(ii) Let suspended particles settle before pouring the water out carefully without disturbing the base.
For precautions to adopt while using chlorine tablets, refer to Q. No. 18.
Question 20 : List three important characteristics of safe drinking water and justify, giving three reasons, why filtration is a good method for making water safe for drinking.
Answer : Important characteristics of safe drinking water are:
Physical Colourless, tasteless, odourless, transparent and having no suspended particles.
Chemical Having neutral pH, Fluoride < 1.0 ppm, Nitrate < 50 ppm and other soluble minerals < 1000 ppm.
Biological Having no organic matter, micro-organisms or coliform bacteria.
Filtration is a good method of making water safe for drinking because:
(i) It removes all suspended impurities in the water.
(ii) It removes chemicals, pesticides, herbicides, solvents and chlorine from the water.
(iii) It removes all colours and odours from the water.
4 Marks Questions
Question 21 : What are the household methods for purifying water? Write the benefits and drawbacks of boiling of water for purity at home.
or
Are household methods good enough to provide us safe water?
Answer : Some household methods for purifying water at home are:
(i) Boiling
(ii) Filtering
(iii) Four pitcher system
As these are done by hand, we can categorize them as physical methods.
There are some chemical methods also i.e.
(i) Use of alum
(ii) Chlorine tablets
(iii) Bleaching powder
Some more methods of purifying water come under the category of mechanical methods. They are:
(i) Special stainless steel filter
(ii) Zero B Filter
(iii) UV filter
(iv) RO filter (Reverse Osmosis)
Very commonly used is the boiling method for purifying water for household purposes. In this method, water should be boiled for a minimum of 10 minutes at 100 degree celsius. Water becomes tasteless after boiling, as there is absence of dissolved air in it. Water should be poured in another container to improve its taste.
Benefits of boiling method are:
(i) It is easy and convenient.
(ii) Temporary hardness and salinity of water is also reduced on boiling.
(iii) Solids substances like chalk powder, carbonic compounds and pathogenic micro-organisms are destroyed by boiling.
Drawbacks of Boiling method are:
(i) It is an expensive method, as too much fuel is needed to boil the water.
(ii) The method is time consuming, as it takes time to boil and cool down the water before it may be consumed.
(iii) Boiling makes water tasteless.
Question 22 : You are having a large gathering in your house. To provide safe water for drinking, which method would be more suitable. Boiling or using chlorine tablets? Provide all the details of the method you choose and give one reason why this method is more suitable.
Answer : If we are having a large gathering at our house, the best method to provide safe water for drinking is by using chlorine tablets. The boiling method is time consuming and requires lot of fuel.
In the process of using chlorine tablets to purify the water we must keep in mind the ratio of water to the number of tablets. Usually one tablet of 4 mg is stirred and dissolved in one litre of water. The bottle cap is left loose to allow a little leakage. After 3 minutes the bottle is shaken and some water is allowed to leak out. The cap is then tightened and left for 10 minutes before the water is ready to be consumed.
This method is more suitable for large gathering as it is very cheap and less time consuming than boiling method. It is safe also as all bacterial contaminants are killed in this method.
5 Marks Questions
Question 23 : Explain the Reverse Osmosis Water Filter process. Why it is a good method? List two of its drawbacks.
Answer : The Reverse Osmosis Water Filter Process removes not only bacteria but also dissolved impurities from water. The process consists of a 5 stage water purification system where impurities from water. The process consists of a 5 stages water purification system where impurities or contaminants get removed at every stage.
These stages are:
(i) In the first stage, water is purified by filtering it through a sediment filter which helps in removing dirt, sand, etc.
(ii) Next, an activated carbon filter is used to trap organic chemicals and chlorine.
(iii) In third stage, molecules are forced through a semi-permeable membrane to remove hard chemicals and minerals.
(iv) Next, another activated carbon filter is used to trap organic chemicals and chlorine.
(v) In the final stage, the water passes through an ultraviolet light which kills the microbes which might have escaped other membranes.
Use of RO system for purifying water is considered on of the most cost effective methods in the long run. It is designed to remove not only virus and bacteria but also dissolved impurities like arsenic, fluorides, heavy metals, rust, pesticides, etc.
Advantages of RO system are:
(i) RO membrances can last long (15 years).
(ii) Filter needs minimum maintenance (once in a year).
(iii) Water is free of all contaminants.
(iv) Membrances can be easily cleaned.
Drawbacks of RO system are:
(i) It is expensive initially; nor everyone will be able to afford it.
(ii) About 50% of the water is wasted as it drains away alongwith the impurities.
Question 24 : What is the importance of potable water for good health? What type of impurities may be present in water?
Answer : Water which is free from impurities and is safe for drinking is known as potable water. It is very essential to avoid drinking dirty water as it may cause many diseases such as cholera, diarrhoea, dyssentry, jaundice, typhoid, etc. Moreover impurities such as straw, wood or sand present in the water may cause damage to our intestines leading to health problems. The types of impurities present in water can be:
Impurities from the Source of Water From the glaciers water melts and comes through hills and valleys to rivers. When river flow through plains, waste of factories, and soluble salts of calcium and magnesium in it create problems in digestive system. Washing of clothes in ponds, bathing animals in ponds, etc pollutes water.
Suspended Impurities Pathogenic organism and their eggs pollute the water which mainly affect our digestive system.
Sand, soil particles, leaves, straws, etc make water impure. Water polluted by industrial pollutants like lead, zinc, chromium, nickle, etc adversely affect human body.
Impure Water due to Other Factors Drinking water may get contaminated due to mining of fresh water line with sewer line. Water from taps can be stored in contaminated utensils. Water stores in pitchers may absorb dust and microbes through its pores. If water is stored in metal utensils, it does not get fresh air and after some time it becomes impure. Generally, pipes made of lead or other metals are used for the supply of water. The chemical reaction of water with these metals also makes the water impure.
So, it is necessary to know and avoid impurities of water and consume pure water. Water borne diseases can be avoided if we pay attention to consume only safe drinking water.