Portsmouth Water

Farlington Treatment Works

The Farlington Treatment Works is owned and operated by Portsmouth Water. Pumping to the site from Farlington began from Havant in 1860 using steam driven engines. The plant now treats water from the Havant and Bedhampton Springs, producing on average 30% of the water supplied by the Company. Following extensive modernisation its staff has been reduced from 19 to 3.

Havant Springs

The water treated at Farlington comes from a set of natural springs, near Langstone Harbour in Havant. This supply is considered the largest of its kind in the United Kingdom - 23 of the springs are used. The yield can vary significantly; seasons of high rainfall can increase it to 160 million litres, drought can decrease it to 53 million litres.
These springs provide 30% of water supplied by Portsmouth Water Ltd.

Pumping to Farlington

The spring water has to be pumped 3km from Havant to Farlington and this is done by electric pumps at 2 nearby pumping stations. If these fail, a third station has diesel-powered pumps as a standby. The water receives an initial chlorine dose as it begins the journey to Farlington.

The Treatment Process

The treatment process at Farlington Water Treatment Works is outlined in the diagram below:

Stage 1
Spring water is collected at Havant and Bedhampton, dosed with chlorine to begin the disinfection process and pumped by High Lift Pumps to Farlington Water Treatment Works.

Stage 2
Partially treated water enters the Splitter Weir Chamber where, if necessary, alum is added to aid the filtration process. Here the flow is split with one third of the flow going to Stream 1 and two thirds to Stream 2.

Stage 3
The partially treated water passes to the Flash Mixer where the alum, a coagulation aid, starts to bind together the small particles which cause turbidity.

Stage 4
The coagulated water is then divided equally between five Rapid Gravity Filters in Stream 1 and eight Filters in Stream 2. Here the water is filtered through a graded sand and gravel bed, approximately one metre deep, before being discharged to the filtered water channel below.

Stage 5
Following filtration, the chlorine dose in the 'final water' is adjusted to its set point and it flows into the Contact Tank.Stage 6
After a minimum of 10 minutes contact with the chlorine dose, a number of monitoring checks are conducted before the water is transferred from the Works to underground service reservoirs nearby.

Filter Cleaning

After a few days, filters start to become blocked by the solid particles they remove from the spring water. They are cleaned by a special process, which can be started either automatically by the sensors in the filter itself, or by manual pushbutton operation by the Companys Superintendents. Filter cleaning is carried out with air and water by closing the filter water inlet and outlet valves. The process and description are shown below :

8. Compressed air is bubbled upwards through the filter bed for approximately 5 minutes.

9. Wash water is passed upwards via the filtered water channel, through the filter bed for approximately 3 minutes.

10. The wash water drains away through an outlet valve flushing the surface of the filter as it flows out. The filter inlet valve is then opened, the filter refills and is returned to service.

Technically Speaking... Abbreviations used are as follows:
Ml	megalitres (1Ml = 1000000litres)
Ml/d	megalitres per day
HP	horse power
mm	millimetres
mm/sec	millimetres per second
m	metres
mg/l	milligrams per litre

Quality Assurance

The Farlington plant has a range of features which ensure the quality and supply of the filtered water.

The chlorine level is carefully monitored to ensure a safe water supply and should the water be turbid after heavy rain, alum is added to make the dirt form a surface layer which is then easily removed.

Two day's water supply is always held in reserve, to cover changes in demand and there is an overflow reservoir to prevent flooding.

The plant has an emergency generator in case of power failure, and automatic warning systems both at the works and at the Operations Centre at Havant.

Farlington History

The story of Farlington begins in 1812 when Thomas Smith built a reservoir to hold spring water from Farlington Marshes. The original filtration works were constructed in 1908, and by 1924 had 5 reservoirs and 8 slow sand filters. The first bank of 5 rapid gravity (stage 1) filters were installed in 1965. Complete modernisation of the works took place between 1978-1982. During these 4 years another bank of 8 rapid gravity filters (stage 2) was added, the slow sand filters were abandoned and a covered 40 million litre reservoir was built. Farlington now has 13 rapid gravity filters and 6 part-buried covered service reservoirs.