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- Water Treatment
The process of taking rainfall and turning it into potable (drinkable) water that flows from your tap appears deceptively simple. When treating stream water supplies and stored water intended for human consumption, it is absolutely vital to ensure that the final product is safe, wholesome and conforms to the latest United Kingdom drinking water standards.
Rainwater may appear to be clean, but by the time it has absorbed or dissolved a host of compounds, dirt and dust from the air, run off buildings, streets and across muddy fields, it is far from pure. The following describes the basic principles of water treatment, which takes you through the steps of collecting rainfall, storing it, treating it, and distributing it to our customers.
You can view the conventional water treatment process using our interactive graphic below, this graphic illustrates our Juas Water Treatment Works, but this process is also used at Kings Mills Water Treatment Works.
Juas Water Treatment Works
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This infographic is optimised for use on larger screens but you can still explore the treatment works by tapping on the individual elements in the illustration below. For an optimal experience, we recommend browsing with a larger screen.
This is where all the water treatment chemicals are stored and prepared for dosing. We also produce Sodium Hypochlorite here, a disinfectant which is added as a final dose to the filtered water, ensuring acceptable water quality is maintained as water travels though the distribution network to customers' homes.
The water treatment works is controlled remotely from our HQ at Brickfield House. However the water treatment works can also be operated from the control room on site. The control room is also home to many instruments that measure and report the quality of the water in real time to our operators.
Juas water treatment works is home to Guernsey Water's third largest storage reservoir, a combination of three quarries, Queens, Juas and Hougue Juas. These reservoirs join when the water level is above 11 metres. Storage is important & helps reduce nitrate and bacteria levels in the water naturally prior to treatment. Water is pumped from these quarries into the clarifier tanks where the treatment process begins.
The first treatment stage involves the removal of dirt aided by the addition of a small volume of two chemicals, a flocculant and clarifier aid, these allow for efficient settling of solids (bacteria / viruses / dirt) from the water in the clarifier. The 'clarified' water then flows to the filter house for additional treatment. The clarified solids and chemical dose are decanted from the clarifier periodically and pumped to waste via our sewer network.
Water flows from the clarifier to one of three rapid gravity sand filters, these dual media filters (sand / anthracite) further remove suspended particles. The water exits the bottom of each filter and flows into the clear water tank. Periodic washing of the sand filters takes place to clean them, the water from this process is recycled back to the reservoir following solids removal in the wash-water recovery tanks.
Washwater Recovery Tanks
Particles captured in the filter beds are periodically washed out, this washwater, containing the particles, is then gravity fed into three of the site's washwater tanks, where the sediment settles out to form a layer of sludge. The sludge is then pumped into the sewer network and the remaining water returned to the quarry for future use.
High Lift Pump House
Home to the pumps which feed treated water into our distribution network. Clean water from the filter beds flows to the high lift house where it is treated with ultraviolet light for disinfection and a final dose of chlorine. This ensures wholesome water quality is maintained as it travels through the distribution network to customers' homes. Water samples are taken on a regular basis at this point.
These treated water storage tanks provide a simple way to control constant pressures within the distribution network during fluctuating water demands during the day and also provide a short-term supply facility in times of emergency breakdown of pumps or other treatment equipment.
Powdered carbon can be added to the water feed before reaching the clarifier tank to improve the taste of the water during spring and summer algal bloom activity. Algal blooms can impart odd tastes to the water supply on occasion. The powdered carbon is then removed in the next stage of treatment - clarification.
Random samples are taken from our customers' homes throughout the year to ensure that water quality meets our standards. 1236 individual tests were conducted in 2017.