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The Island has six Raw Water Storage Reservoirs located at:

• Val de la Mare
• Queen’s Valley
• Handois
• Millbrook
• Dannemarche
• Grands Vaux

The reservoirs store untreated water collected from streams and pumped from the raw water abstraction points and the desalination plant.

Each reservoir has a catchment area, the size of which depends on the geography of the surrounding countryside. Rainfall in a catchment area runs off the land into streams which feed the reservoir. Unusually,
in Jersey a number of the catchment areas generate more water than can be stored in the respective reservoir. To overcome this problem and fully utilise the reservoir and catchment area capacity, a system
of raw water transfer mains has been developed which allows water to be moved between the reservoirs. When one reservoir is full, water can be moved to a second reservoir so that the first one can keep filling.

When full, the reservoirs hold enough useable water to provide approximately 110 days of supply to the Island. All reservoirs are equipped with monitoring equipment allowing water levels and certain quality parameters to be continuously monitored. In addition, samples are regularly taken from the reservoirs for analysis in the Company’s laboratory.

When required for treatment, the stored water is pumped from the reservoirs to either Handois or Augrès Water Treatment Works. Water is specifically selected from the reservoirs so as to provide the best quality
water at any time.

Both Queen’s Valley and Val de la Mare reservoirs are open to the public. For further details (click here).

Type of construction	Catchment area (hectares)	Max capacity (megalitres)	Max capacity (million gallons)	Top Water Level (mAOD)	Length of dam (metres)	Max height of dam (metres)	Maximum depth of water (metres)
Dannemarche St Lawrence - 1909
Masonry faced, mass concrete infill	200	93.0	20.46	45.26	70.1	7.9	6.5
Grands Vaux St Saviour - 1952
Mass concrete	909	229.6	50.5	36.58	141	15	9.5
Handois St Lawrence - 1931
Masonry faced, mass concrete infill	271	187.5	41.25	88.70	110	7.3	4.0
Millbrook St Lawrence - 1890
Masonry faced, mass concrete infill with clay core	127	36.4	8.0	19.83	57.3	6.0	3.5
Queen’s Valley Grouville - 1991
Rockfill embankment with bituminous concrete core	516	1193.0	262	36.00	175	24	20
Val de la Mare St Peter/ St Ouen - 1962
Mass concrete	350	938.7	206.5	46.02	192.9	32.81	24.31