Chennai formerly known as Madras, the capital of Tamil Nadu is the sixth most populous city in India with 4.68 million residents as of 2011. Until 1870, it had no piped water supply within the city and people were dependent on public and private wells. The construction of a piped water supply system was started in 1872. This laid the foundation for the present water supply system. Today, Chennai Metropolitan Water Supply and Sewerage Board (CMWSSB) looks after the drinking water supply of the city.

Due to absence of a perennial river within the city, Chennai is dependent on rainfall and ground water. At present flood water from three rivers namely Kortalayar, Nagari and Nandi are collected in Poondi, Cholavaram and Red Hills reservoirs. Water from these reservoirs is then sent for treatment to the Kilpauk and Red Hills water treatment plants. There, the supply is augmented with ground water from six wells located in Kortalayar Araniar basin. There are six wells from which a total 100 million litres per day (mld) of ground water is extracted.

Following Figure-1 is a simplified pictorial representation of the drinking water supply system of Chennai city.

The Kilpauk treatment plant was the first of its kind to be established in the city, with a design capacity of 270 mld. The Red Hills water treatment plant was constructed in 1996 with a treatment capacity of 300 mld. All the basic water treatment procedures are carried out in both treatment plants. Also both treatment plants have well equipped laboratories in which physical and chemical tests are carried out to keep a check on the water quality.

Water from these two water treatment plants is supplied to 16 distribution zones within the city. From here, drinking water is supplied to various parts of the city. The sixteen water distribution zones have been shown in the following figure-2.

The National Environmental Engineering Research Institute, Nagpur in 2002 had carried out water quality checks at all the stages namely source, treatment level, service reservoir level and at the consumer level during the monsoon, summer and winter seasons. (See data here). Water samples from sources viz. Poondi lake, Cholavaram lake, Chembarambakkam lake, Red Hills lake and Porur lake were monitored once for all water quality parameters. Samples were also collected from service reservoirs and analysed for residual chlorine and bacteriological contamination. Both the treatment plants were evaluated unit wise on three different dates at various stages of treatment system. The parameters analyzed were Turbidity, Total Coliforms (TC) &Total Faecal Coliforms (TFC). 

The complete results are attached in the annexures section. Below is a short analysis. 

• Source Level

The water quality of Cholavaram, Poondi, Porur and Chembarampakkam lakes are within desirable limits for all parameters except for TC and TFC. Both these are present in large amounts during all the three seasons. The graph below (Figure 3) depicts the concentration of TC in the lake water.

The  concentration of TC during summer, monsoon and winter in Poondi, Porur and Chembarambakkam lake is so large that the concentration has been designated as “too numerous to count”. So the columns depicting the concentration of the above mentioned samples have been shown with a black bar (                  ). The concentration of TFC during the three seasons for Poondi, Porur and Chembarambakkam lake have been depicted in Figure-4.

As for surface water source, Dissolved Oxygen (DO) and Chemical Oxygen Demand (COD) have been considered for the lakes. DO is an important characteristic depicting the oxygen concentration present in a water body required for sustaining aquatic life. The permissible limit for DO is 4 milligrams per litre (mg/l).

On the other hand COD values indicate the amount of oxygen required to disintegrate all the organic mater (carboneous and non carboneous) into carbon dioxide and water. As the water from the source is treated and disinfected before being  supplied as drinking water, it is equivalent to Class C water body (drinking water source after conventional treatment and disinfection). Thus, according to World Health Organization (WHO) guideliness, the COD permisible level should be 10 mg/l.

• Treatment Level

The treated water samples are within the desirable range of the BIS 10500 specification for drinking water except for bacterial parameters. It has been observed that 3 out 4 samples taken from the Red Hills plant are contaminated with bacteria but only 1 out of 4 water samples from the Kilpauk plant is contaminated. Figures 7 and 8 below show the level of TC and TFC in the treated water for the three seasons. The permissible level of TC and TFC in drinking water sample should be 0 mg/100 ml.

Apart from bacterial contamination, two out of three outlet water samples from the Red Hills plant during the winter season have shown high TDS level of 570 mg/l and 505 mg/l against the desirable limit of 500 mg/l.

• Service reservoir level

At the service reservoirs level the presence of bacteria depends on the amount of residual chlorine present. Some samples having residual chlorine concentration well above the minimum limit of 0.2 mg/l and have shown the presence of TC and TFC. The following map highlights the areas receiving contaminated water during different seasons.

Also the population of people receiving bacterial contaminated water differ during the three seasons. In summer 6 out of 16 zones with a population of 29 lakhs out of 50 lakhs are receiving contaminated water, while in winter 7 zones (population 16 lakhs) and during the monsoons only 2 zones (population 6 lakhs) receive contaminated water. So the percentage of population receiving contaminated water in summer and winter is higher than during the monsoons. 

• Consumer End level

The water from the service reservoir is then distributed to the consumer end through pipelines. The above graph (Figure 11) shows that 59% of places are receiving contaminated water in summer and monsoon while only 54% of places are affected in winter. Thus in all the seasons more than half of the city is receiving contaminated water.

Apart from the bacterial contamination, the quality of drinking water is within permissible limits of BIS drinking water standard IS 10500.

Discussion

From the about results the following points can be analysed.

At the source level:

• DO level of all the lakes in all the seasons are above 4mg/l (minimum DO level required for a water body) thus indicating that the lakes are not too polluted with organic matter. If there is sudden load of organic matter then there is plenty of oxygen concentration for its decomposition. Also the graph (Fig-5) indicates that DO levels in the monsoon are high, which could be due to dilution of rain water and aeration caused during rainfall. Summer and winter DO levels are of the same range as of each other (8-6 mg/l) and are satisfactory.
• COD of the lakes varies from 20 -50 mg/l (Fig -6) against the desirable limit of 10 mg/l. This data isn't available for the winter season. In the monsoon the levels are much higher than in summer. This could be due flow of runoff with garbage into the lakes from nearby area.

Reports of pollution in Porur and Poondi lakes have been published from time to time by both national and regional newspapers in the city. Apart from the garbage dumps at the lake side, spreading of water hyacinth in the lakes has been reported by The Hindu. Chembarampakkam lake receives effluents from surrounding industrial area. Timely action by the municipal department should be taken to prevent further pollution of the water sources.

At treatment level:

• Bacterial contamination is the main problem; all other test parameters are within the desirable limit. Presence of bacteria after treatment can be attributed to the insufficient contact time of chlorine and water. More contact time of residual chlorine with water will insure more disinfection. This drives our focus to the negligence caused by the department in water purifying. Bacterial contamination makes the water unfit for consumption.
• High TDS value is found in the treated water samples from the Red Hills plant. The reason for this is that the groundwater mixes with the surface water. According to a report in Times of India (Chennai edition) of 19th April 2011 TDS content in the groundwater has increased due to salt water intrusion from the sea. 

At Service reservoir level:

• Bacterial presence at this level has been linked to insufficient contact time between chlorine and water, which is preventing better disinfection. The concentration of residual chlorine is well above 0.02 mg/l.

 At Consumer end level:

• Leaky water distribution pipes have been identified as the cause of bacterial contamination at this stage. The pipelines are 100 years old and at several places have been affected by rust thus leading to leakage. Lack of maintenance has led to mixing of sewage water with drinking water thus contaminating the drinking water supply with TC and TFC. 
• Leading news paper like The Hindu and The Times Of India have reported that tap water of places like Tondiarpet, Pulianthope, Basin Bridge, Ayanavaram, Nungambakkam, Kilpauk, Kodambakkam, Ice House, Saidapet and Adyar is unfit for consumption. In these places bacterial contamination have been found in the drinking water samples collected by NEERI. Also local people from these regions have complained that the water from the tap stinks and is unhealthy. Diseases like diarrhoea, urinary tract infection, cholecystitis, bacteremia and cholangitis are caused by drinking water contaminated with E.coli.

 Conclusion

From the above discussion we can say that bacterial contamination is the problem affecting more than half of the city. Residents have to install water purifires. This puts a strain on lower income groups as they have to install water purifiers and also pay for water tax. The price of water purifiers available in the market ranges from Rs. 700 to 6000 in addition to maintainence costs. Apart from this, consuming contamiated water gives rise to many diseases like diarrhorea, urinary tract infection, cholecystitis, bacteremia and cholangitis. Thus their health is also affected and money is spent on health checkups.

To improve the water quality and to increase the water supply across the city, Chennai Metro Water Department have taken the following steps:

• Improvement in the water quality and supply

Chennai Metro Water department had previously prepared a master plan for water supply in 1978, which was updated in 1991. This was knows as the First Chennai Project. Increase in water supply and water treatment capacity was the main motive for the 1991 project to meet the needs of the city's increasing population. With aid from the World Bank the project, which also included renewing old and choked pipelines was implemented.

In 2004, the Second Chennai Project was completed with the assistance from the World Bank. The first phase included increase in piped water supply availability and improvement in service levels in some areas.

The last part of the project was taken up by Chennai Metro Water Supply and Sewage Board and was implemented under 13 packages with fund from JNNURM, which included work for improving water distribution system in all the zones, leak detection and rectification programmes .

Action Points:

Though Chennai Metro is expanding to provide drinking water, the main challenge is to provide uncontaminated water to the consumer. This can only be achieved if both the drinking water supply pipelines and the sewerage pipelines are renewed and maintained to avoid contamination. Below are some of the action points that the Chennai water works department should consider to reduce contamination:

• Cleaning of surface water source

Surface water sources should be cleaned from time to time to ensure DO levels are above 4 mg/l. Also the municipal department should keep a check on the garbage dumps around the lake and the effluents entering the lake.

• Maintanance of existing water pipeline

As in the consumer-level bacterial contamination is mainly due to mixing of sewage water so repairing of the pipeline should be the top priority. This will have a positive effect on the water quality as bacterial contamination will not happen.

• Proper Disinfection 

Enough time should be given for the chlorine and water to mix so that the disinfection is complete. This will increase the contact time of residual chlorine with the water, which will help to maximize the disinfection of the water.

• Water Quality Checks

Frequent water quality checks at all the levels ( treatment, service reservoirs, consumer end) should be done to maintain the water quality. CMWWSB should carry out these checks as this will help to upgrade their system and know and check the source of contamination.

• Sustainable Use of Rain Water

Rain water harvesting should be promoted at a household level. This initiative will not only help curb the issue of water shortage but will also prevent contamination. As consumers can store and disinfect the water on their own this will prevent diseases caused by bacterial contamination.