Water Treatment
Longue Hougue Water Treatment Works
The new water treatment plant at Longue Hougue was officially opened by the Bailiff on Monday 22nd June 2009.
Guernsey Water has overseen the construction of the plant by UK-based contractors Enpure Ltd, the successor company to Purac Ltd who built the works at St Saviours. The new plant has cost less than £5 million, which represents exceptionally good value for money when compared with similar facilities elsewhere.
The plant incorporates some of the most technically advanced water treatment processes anywhere in the world and builds upon the experience gained at our St Saviours works. The ultra-fine-filtration membranes are similar to those that have been in successful operation at St Saviours for the last five years and this will ensure the continuing water quality improvement in the Island. To get an idea of how fine the membrane pores are, please click here to see a diagram of particle sizes that are filtered by different treatment processes.
Despite being able to produce 15 million litres of high quality drinking water per day, the new works have been constructed on a remarkably small area of land, with the main processes housed within an existing warehouse structure.
The Longue Hougue water treatment works will generally supply water to the northern and central areas of the Island, while St Saviours will feed the rest of the Island. The water treatment works at Kings Mills will remain as back-up in case of exceptional summertime demand, or in the event of essential maintenance at either of the other two mainstream works.
Guernsey Water has also been able to enlist the services of a number of local companies in constructing the new plant. The likes of Ronez, Greg Forino Flooring and Geomarine have demonstrated that there are many skilled craftspeople within the Island, and their involvement has been vital to the successful completion of the project.
The Water Treatment Process
The process of taking precipitation and turning it into drinkable water that pours out of your tap is a complex one. When dealing with anything that is for human consumption, it is absolutely vital to ensure that the product is thoroughly cleansed and is free of any contamination.
The diagram below demonstrates the water treatment process, which takes you through the steps of collecting rainfall, storing it, treating it, and distributing it to our customers.
It is important that Guernsey Water collects as much precipitation that falls to the ground as possible. Annual rainfall levels can vary substantially, and a dry winter can have a negative impact on the island’s water resources.
The impact of global warming on the climate will start to produce different weather patterns in the future, and Guernsey Water must ensure that they are able to collect, store and treat as much rainfall as possible. The expansion of the Water Catchment Area is one method of increasing the amount of water collected.
Guernsey Water staff work closely with horticultural and agricultural bodies to ensure that potential pollutants such as herbicides and pesticides are not allowed to contaminate the water supply. By taking a proactive approach, monitoring the Catchment Area acts as a first defence in protecting Guernsey’s water supply. The Catchment Area measures over 43km², and takes up much of the island.
What many people don’t realise is that water being stored is also starting the treatment process - wave action and ultraviolet light from the sun removes some impurities from the water. Guernsey Water oversees 18 quarries and storage reservoirs.
Method 1 is used at Kings Mills, where water is pushed through a large ‘sieve’ to remove leaves etc. Added chemicals then clarify the water by causing particles to stick together, creating a layer of ‘floc’ which floats & is removed. After filtration through sand to cleanse it further, the water runs through a ‘contact tank’, which disinfects the water to ensure that it remains pure through the pipe network to customers’ taps.
Method 2 utilises state-of-the-art membrane tubes with ultra-small spaces - the water is able to pass through the membrane, but impurities are left on the outside of the tubes and removed as ‘sludge’. St Saviours and Longue Hougue WTW use this technology.
When required, the water travels through 400kms of distribution pipework, to customers’ houses. A stopcock valve controls the water flow from the distribution pipe to a service pipe which delivers the water to customers’ taps.
Samples are taken from Catchment Area streams, WTW’s, service reservoirs, the distribution network and customer taps. 99.86% of samples in 2009 passed the strict criteria - a very impressive result that stands comparison to anywhere else in the UK or EU.