Information Centre Greater Colombo Water Supply Scheme 
 
Greater Colombo Water Supply Scheme
           
           
Ambatale Water Supply Scheme
           
Year Commissioned : 1966 (Old Plant)      
  : 1994 (New Plant)      
           
Water Source : Kelani River      
           
Water Intake : 02 Pump Houses ( Old & New)      
  : 577,000 cum per day      
           
Sedimentation Tanks : 05 Tanks capacity 61,300 cum each      
  : 04 Tanks capacity 45,000 cum each      
           
Filters : 26 (18+8) Rapid Gravity Sand Filters      
           
Chemicals : Alum Al2(SO4)3. 14H2O      
  : Lime Ca(OH)2 Chlorine gas Cl2      
           
Water Storage : 03 Tanks (91,000; 4,200; 6,600 cum)      
           
Production per day : 470,000 cum (105 million gallons)      
           
Production Capacity (maximum) : 500,000 cum per day      
           
Kalatuwawa Water Supply Scheme
     
Year Commissioned : 1960      
       
Water Source : Kalatuwawa Reservoir      
       
Water Catchment Area : 3500 Acres      
       
Water Surface : 320 Acres      
       
Dam     - Length : 980 feet      
- Height
: 80 feet      
       
Maximum Water Level : 370 feet MSL      
       
Water Intake : Water flows to Treatment Plant under gravity      
       
Sedimentation Tanks : 02 Tanks Horizontal flow      
       
Filters : 10 Rapid Gravity Sand Filters      
       
Chemicals : Alum, Lime and Chlorine      
       
Power Generators : 02      
       
Transmission Lines : 02      
       
Production per day / Distribution : 68,000 cum      
           
Labugama Water Supply Scheme
           
Year Commissioned : 1960      
       
Water Source : Labugama Reservoir      
       
Water Catchment Area : 2500 Acres      
       
Main Dam - Length : 420 feet      
       
Reservoir Dam Height : 87 feet      
       
Maximum Water Level : 370 feet MSL      
       
Water Intake : Water flows to Treatment Plant under gravity    
       
Sedimentation Tanks : 02 Tanks Horizontal flow      
       
Filters : 15 Jewel Type (Circular) Sand Filters      
       
Chemicals : Alum, Lime and Chlorine      
       
Transmission Lines : 03      
       
Production per day / Distribution : 38,000 cum      
       
Maximum Production Capacity : 53,000 cum per day      
           
Water Treatment | Greater Colombo Water Supply Scheme
           
Question 1 : How does Greater Colombo gets its drinking water?
Response The Greater Colombo area get its drinking water from:
i) Ambatale Water Treatment Complex
ii) Kalatuwawa Treatment Plant
iii) Labugama Treatment Plant
           
Question 2 : From where do the Treatment plants get its water supply?
Response Ambatale Water Treatment Plant - From the Kelani River
Kalatuwawa Water Treatment Plant - Kalatuwawa Impounding Reservoir
Labugama Water Treatment Plant - Labugama Impounding Reservoirs
These water sources are surface water.
           
Question 3 : The Treatment Plant get the water from the Water Source. But the water source is not near. How does the water enter the Plant?
Response Ambatale Treatment Plant - Pump from the Kelani River by the two 2 pump houses on the left bank of the Kelani River. These pumps work 24 hours. Therefore a large sum of money has to be spent on electricity.
Kalatuwawa & Labugama Plants - Receive Water under gravity
           
Question 4 : Is this the water you distribute?
Response No !
  • The water that is found in the rivers & reservoirs are usually not suitable for drinking.
  • The water in the Kelani River is polluted by the activities of man & animals.
  • The effluents of the industries situated along the river, domestic wastes,
    • storm water, and sewage-all enter the river through a system of drains & waterways.
  • Hence the river water is not suitable for drinking.
    		•
               
    Question 5 : How do you purify your water?
    Response The Purification or the Treatment process consists of 5 steps.
    They are:
  • Aeration
  • Addition of chemicals
    		• Coagulation
    Flocculation
  • Sedimentation
    		•
  • Filtration
    		•
  • Disinfection
    		•
               
    Question 6 : Can you describe these steps please?
    Response First Step - Aeration process.
  • Air (oxygen) is introduced into water.
  • By this means, the taste, colour and odour causing substances and gases are removed.
    		•
               
    Question 7 : Next step please?
    Response Second Step - Addition of Chemicals.
  • The chemicals we use are Lime and Alum.
  • We import these chemicals from foreign countries. Therefore it is expensive.
  • When chemicals are added to water, it reacts with soil & clay particles, microorganisms &
    • other substances.
  • This is called Coagulation.
  • These particles associate with similar particles to form big flocs.
  • The process is called Flocculation.
  • The flocs when it is heavy sink to the bottom. The result is clear water at the top.
    		•
               
    Question 8 : Are chemicals added in measured quantities?
    Response Yes.
  • We carry out a Jar Test in the Laboratory to find out the dosage required.
  • We add measured amounts of chemicals to a known volume of water to find out which alum & lime dosage forms a good floc
    		•
  • At the Plant, these dosages are added proportionately to water.
    •            
    Question 9 : What is the third step in water treatment process?
    Response Third Step - Sedimentation Process.
  • The flocs as stated above, are formed in large sedimentation tanks.
    		•
  • These Clarification Tanks are called
    •       - Pulsators,
          - Pre-treaters and
          - Centriflocs.
  • Clear water is found at the surface of the tanks.
  • This water is sent into the sand filters through a network of channels.
    		•
               
    Question 10 : The fourth step in the Treatment process is Filtration. What happens here?
    Response Fourth Step - Filtration
  • Water is filtered through the Rapid Gravity sand filters.
  • At Ambatale, there are 26 filters.
  • The suspended solids & some microorganisms are removed by this process.
    		•
               
    Question 11 : Can you use these Rapid Gravity Sand filters continuously?
    Response No!
  • When the interstices of the sand filters get blocked, the filtration rate reduces.
  • Then we wash the filters.
  • It is called the "back washing"
    •       - First compressed air is sent through the pipelines laid down at the bottom of the filters.
          - This is followed by treated water till the muddy and waste particles are removed.
          - To wash one filter, 365 cum (8100 gallon) of treated water is used.
             
    Question 12 : Next is the disinfection process, isn't it?
    Response Fourth Step - Disinfection
  • This is the last step in the water treatment process.
  • This is also called Chlorination as we use Chlorine gas to disinfect water.
  • Chlorine is a strong oxidizing agent and it destroys pathogens- that is disease causing organisms
    • like Bacteria remaining in the water.
               
    Question 13 : All right. Does the water contain Chlorine always?
    Response Yes mostly. We try to chlorinate the water so as to maintain residual chlorine in the water.
    "In fact, having residual chlorine in the water is like having an army.When germs (enemies) are found in the water, the residual chlorine attacks it and destroys it. It is just like an army meeting enemies!"
               
    Question 14 : Is the water safe to drink now?
    Response Yes
  • But we add another chemical to water.
  • It is lime. We need to maintain a certain alkalinity in the water.
  • We call it Post lime addition.
  • It prevents corrosion of the distribution lines.
    		•
               
    Question 15 : This must be safe water?
    Response Of course yes! This is safe water.
    Safe water is really water that
          - Does not contain any disease causing organisms
          - Does not contain chemicals hazardous to human health
          - Water is clear, colorless, tasteless and odorless and
          - It does not stain or get precipitated.
               
    Question 16 : Well Thank you. Here's a question on payment. Water is taken from the rivers free of charge. So why do you charge us a big fee for using water?
    Response 'Dear children, we can't use river water as it is for drinking. First we have to pump the water to the Treatment Plant, and then treat it with chemicals, which we import to remove impurities and disinfect it to make it safe. We also monitor the water quality and transport it to your houses. As you are now aware a large sum of money is needed to do it.
  • National Water Supply & Drainage Board, in the year 2008, spent Rs.45 million monthly to produce 17 million cum of water.
  • That is, to produce 1000 Litres, it cost Rs.2.65.
    		•
    The break up of monthly Production cost is as follows:
    Electricity 71%
    Chemicals 10%
    Administration/ Salaries/ Repairs/ Security/ Others 13%  
    Now you can see how expensive it is to produce safe drinking water. To cover our expenses we are compelled to charge a fee for the water you use.
    If you use water carefully and prevent wastage you can reduce your water bills.
               
    Question 17 : Oh... then we too have a role to play! We must learn to use water without wasting it?
    Response Yes definitely. In short, if you attempt to do the following the benefits we - our country, you and I can achieve are immense.
    1.
    		To use water carefully without wasting.
    2.
    		To keep tap closed when brushing teeth, washing face or doing work in the kitchen.
    3.
    		To use water saving techniques to reduce the usage of water. Have a bottle/bag full of water in the Toilet cistern; have a faucet aerator installed in the taps to reduce flow.
    4.
    		To protect the water resources. Do not use it as a dumping ground for waste disposal either for domestic or industrial purposes.
    5.
    		To attend immediately to any water Leaks in the house. Inform the Water Board or its  offices, of leaks outside your premises as soon as you detect it. Dial All Island Toll Free Call Centre on 1939 please.
    6.
    		Try to use alternate sources of water other than drinking water for gardening.
    "Dear Parents and Children,
    Though three fourth of the world is covered with water, less than 1% is available for man's use. Even this water is polluted by the activities of man and animals. Therefore in the future, to obtain drinking water a large sum of money will be needed. If you protect your water resources and use only what is required there would be enough water to all - even for future generations. Remember, we enjoy today the water resources protected & conserved by our Great, great grandfathers. "
    'Water is an essential resource. It is our duty to protect & conserve it.'
               
    ::: Updated on 2009.11.12 :::
               
    © 2009 National Water Supply and Drainage Board. All rights reserved.