Public Water Supply System in the Twin Cities
Water Delivery System

Public Water Supply System in the Twin Cities

In this blog, we will be discussing about where Rawalpindi and Islamabad get their water from and how it’s treated. We will also be sharing valuable insights on the Rawal Treatment plant and whether the water treated by it is safe for human consumption or not

Where do the twin cities get their water from?

The main sources of water in Rawalpindi Islamabad are surface water and ground water. Simli Dam and Khanpur Dam are major water resources for the capital city Islamabad together with many tube wells, as water aquifer within the capital region is shallow and scattered. Khanpur Dam too supplies water to Rawalpindi city in conjunction with Rawal Dam. The Capital Development Authority along with surface water, is providing the ground water of 180 tube wells to Islamabad, whereas Rawalpindi Development Authority is providing upto 260 tube wells to Rawalpindi. Private and municipal wells are also utilized to fulfill the water prerequisites.

A map of water sources of Rawalpindi/Islamabad
A map of water sources of Rawalpindi/Islamabad

Who treats this water?

Water and Sanitation Agency(WASA) is responsible for Rawal Lake Water Treatment Plant. WASA falls under the supervision of Rawalpindi Development Authority. The dam intakes water from the Rawal Dam/Lake and treats it for supply to the Potohar region.

A google maps image of Rawal lake on the left and Rawal Lake treatment facility on the right
A google maps image of Rawal lake on the left and Rawal Lake treatment facility on the right

How Water is Treated in the Water Treatment Plant?

The water treatment process begins at the pumping station. Pumps draw raw water from reservoir, lakes, rivers, streams, wells or underground sources. Water travels by pipeline to the water treatment system. The first step in the cleaning process is removing sediments and particles from the water with the help of coagulant. Coagulants are chemicals that act like magnets. They are often added right at the inlet of the water filtration plant. The water then goes into mixing basins called flocculation basins for flocculation water treatment . In these basins, the solution of water and coagulants will slowly be mixed together to form what are called floc particles. After mixing for a set amount of time determined by the water quality in the flocculation basins, the water is moved to sedimentation basins. It’s in these holding tanks where the water sits for the floc particles to begin settling out at a faster rate which is the intended goal of this process. By simply adding and mixing these chemicals into the water and letting that water sit, a large portion of the sediment will settle out to the bottom as sludge which can be taken away to a landfill or holding facility. These floc particles are ultimately removed from the bottom of basins and the clean water, being the cleanest at the top due to the settling particles, flows to the next stage of the process.

After the majority of the solids are removed from the water during coagulation and flocculation followed by sedimentation, the water flows over to the next step i.e filtration.

The water at this point will start looking clear, but there will still be bacteria and very small suspended solids present in the mix. The filtration process in water treatment will seek to remove the remainder of the suspended solids and bacteria to further bring the water up to the snuff. For this process a sand filtration process is used. Sand filters are exactly what they sound like. A basin of fine to coarse sand that filters water. It would theoretically be possible to treat water with only sand filters, but that would result in frequently clogged sand filters resulting in lower efficiency and more cleaning time. Water flowing out of sand filter will need to have a clarity of around less than 0.3 NTU (Nephelometric Turbedity Units).

At this point the water should be crystal clear but their still remains some residual bacteria. This leads us to the next step: Disinfection. There are three main ways of disinfection in the water treatment process which can be used individually or in combination with one another depending upon design. First, chlorine or chloramine treatment. Second, ozone treatment and finally, ultraviolet radiation treatment. The main method of disinfection used in Simli Dam, Rawal Dam and Khanpur Dam is through chlorine water treatment. This disinfection of water by chlorine works to kill microorganisms. One downside to this process is that these chemicals can react with organic material in the water to create disinfection by-products. These disinfection by-products are harmful to human health.

Even with all of this, chlorine is used mainly because how it kills pathogens. It not only kills any pathogens in the water at the plant but residual chlorine also remain in the tap water, killing any contaminants that might get introduced after leaving the plant.

After the water is treated, it is then pumped into the city’s pipe network for delivery to your tap.

Steps involved in Rawal Dam treatment facility
Steps involved in Rawal Dam treatment facility

And that’s how the public drinking water system works. But what are those water towers you see at some places?

Massive pumps at the treatment plant supply pressure to the system through constant operation. Some of this pressure can be stored as elevation in water towers which can give pumps a backup in emergencies. In a lot of cases water towers allow the pumps at the treatment plant to run at a constant rate, which increases efficiency and removes down time problems. This combination of pumps and water towers allows your tap to remain flowing.

So why can’t you drink from tap?

A thorough study and examination of the drinking water quality of Rawal treatment plant was carried out by collecting samples from eight separate locations. It aimed at examining the water quality of Rawal Treatment Plant, its distribution network.and also to determine the potential relationship between the presence of microorganisms and chlorine residual in the network. Quantification methods of chlorine residual, turbidity, standard plate count, fecal and total coliforms by most probable number (MPN) were used. Free chlorine, residual chlorine, chloramines and total chlorine residual were the types of chlorine measured at the sampling stations. The results showed that pH generally ranged from 7.02–7.30, turbidity from 0.34–2.79 NTU, conductivity fluctuated from 359–374 μS/cm (micro siemens per centimeter) and total dissolved solids (TDS) was found to be ranging between 180–187 mg/l (milligrams per litre). Station number seven turned out to be most infected. Total chlorine at station three and six was found to be 0.86 to 1.7 mg/l. Peak standard plate count was 62 colony forming units per ml (CFU/ml) at station number seven. Most of the stations had total coliforms less that 1.1 MPN/100ml except at station three which had coliforms greater that 23.0 MPN/100ml

Rawal dam treatment plant has not had its filter media and rapid sand filter replaced for many years now. Rapid sand filter has lost its efficiency and some of the particles are trapped in the media. Though backwashing is carried out, these particles have accumulated and degraded the media.

Here’s a map of all the water filtration plants in the twin cities. Find out if the one in your vicinity is safe for drinking or not!

A map of water filteration plants in the twin cities
A map of water filtration plants in the twin cities

Leave a Reply