(i) Inorganic impurities - nitrates, phosphates and metals.
(ii) Organic impurities - fruit and vegetable wastes, oil, urea, human faeces, animal waste, pesticides and herbicides

(x) sewage
(a) nitrates, phosphates and metal
(b) phosphorus and nitrogen

Various alternative arrangements for sewage disposal other than WWTP are septic tanks, chemical toilets and composting pits. Septic tanks are suitable for places where there is no sewage system, such as hospitals, isolated buildings or cluster of 4-5 houses. In other methods, the excreta flow through covered drains into a biogas plant. The biogas thus produced is used as a source of energy.

It is a design of a toilet in which humans excreta is treated by earthworms. It is a novel, low wateruse toilet for safe processing of human waste. The operation of the toilet is very simple and hygienic. In this toilet excreta is completely converted to vermi cakes-a resource much needed for soil.

(i) Domestic wastes
(ii) Agricultural wastes
(iii) Fertilizers
(iv) Insecticides and pesticides
(v)Industrial wastes
(vi) Discharge of sewage

The water which is fit for drinking by human beings is called potable water.
Characteristics:
(i)It is transparent.
(ii)It is odourless and colourless.
(ill) It is harmless or free from disease causing bacteria.

Cleaning of water is a process of removing pollutants from water before it enters a water body or is reused. This process of waste water treatment is commonly known as sewage treatment. It takes place in several stages.

We can control pollution by following measures:
(i)By avoiding disposal of industrial and household wastes into river water.
(ii)By avoiding washing of clothes, cleaning utensils and bathing with soap near the source of water.
(iii) By covering the mouth of well so that dust, leaves etc., may not fall into it.

We all have a part to play in keeping our environment clean and healthy. We must shoulder our responsibility in maintaining the water sources in a healthy state. Adopting good sanitation practices should be our way of life. As an agent of change, our individual initiative will make much difference. We can set an example to others with our energy, ideas and optimism. Much can be done if people work together. There is great power in collective action.

This figure shows the supply of drinking water, its processing and its source as well. Functions of each part of the figure.

Yes, chlorine have a peculiar odour which is not worse than wastewater. 

(a) The settled solids that are removed in wastewater treatment with a scraper is sludge.
(b) Water from kitchen which is used for washing dishes is wastewater.
(c) Wastewater released from homes, industries, hospitals and other public buildings is sewage.

Yes, we all have a, role to play in keeping our environment clean and healthy. All of us can contribute in maintaining sanitation at public places. We should not scatter litter anywhere. If there is no dustbin in sight, we should carry the litter home and throw it in the dustbin .

Some organizations offer hygienic onsite human waste disposal technology. These toilets do not require scavenging. Excreta from the toilet seats flow through covered drains into a biogas plant. The biogas produced is used as a source of energy.

The terms like sewage, sewers and sewerage are interlinked with each other because sewage is a mixture of wastewater coming out of homes and other places. Sewers are pipes which carry sewage and sewerage is a network of sewage carrying pipes.