Portsmouth Water has no large raw water storage reservoirs.  It relies almost entirely upon groundwater reserves in the chalk aquifers of the South Downs and abstracts its raw water from wells, boreholes and springs.  It has one river abstraction at Gaters Mill on the River Itchen, a chalk river with a groundwater baseflow.

Those reserves rise and fall with the seasons and so Portsmouth Water pays particular attention to the local hydrogeological data by monitoring rainfall at its Havant Offices, groundwater levels in the chalk at Idsworth on the Hampshire/Sussex border, as well as the total yield from the natural springs at Havant and Bedhampton.

These resources are monitored on a daily basis and reported upon on a monthly basis.  The information here is therefore at times one month behind the most current situation.

The information gathered is reproduced here for information purposes; no guarantee is given as to its accuracy.

<strong>Rainfall at Havant</strong>

The Rainfall Records at the Company’s Head Office at Havant date back to 1886.

The month of August saw greater than average rainfall with approximately 158% of the long term average rain for the month.  Rain fell on 35% of the days, with the maximum daily rainfall approximately 36.8mm on Sunday 26 August 2018.

Total rainfall for the month was 86.1mm, higher than than the 30 year long term average of 54.6mm.

<a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/dailyhav-aug18.png"><img class="aligncenter size-full wp-image-7466" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/dailyhav-aug18.png" alt="" width="1445" height="688" /></a>

<a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/ltahav-aug18.png"><img class="aligncenter size-full wp-image-7467" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/ltahav-aug18.png" alt="" width="1444" height="693" /></a>

<strong>Groundwater Levels at Idsworth</strong>

The Company has groundwater records from the Idsworth Estate Well, north of Rowlands Castle, which date back to 1931.  Water levels in the Well, which is entirely unaffected by abstraction, give an accurate indication of the groundwater reserves of the South Downs.  In the winter, levels usually rise in response to rainfall, whilst during the summer, levels recede as any summer rainfall either evaporates or is taken up by trees and plants before reaching the aquifer below.  Levels can fluctuate by as much as 20m.

The Groundwater level is usually recorded in metres AOD (Above Ordnance Datum), Ordnance Datum principally being equivalent to sea level.

Groundwater levels at the end of September 2017 were below the long term average.  Autumnal rainfall in September, October and November normally sees the rapid recovery of groundwater levels.  Actual 2017 Autumnal rainfall was 62% of the long term average 154mm compared with 250mm.  The month of October being particularly low, 30mm compared with the long term average of 97mm.  Rainfall within our catchment during January, February and March 2018 was 113% of the long term average and saw groundwater levels recover to approximately 25.5%, 1.2m above the long term average.  Despite the particularly low rainfall in June and July, 25mm, compared with 100mm, groundwater levels at the end of August 2018 were at approximately 16.3, matching the long term average.

It is normal for groundwater levels to continue to fall at this time of the year, water levels are below the long term average and considered to be at “low” levels for the time of year.  So long as rainfall remains close to average for the year, we do not see the need for drought control measures, such as temporary use bans, but would encourage all customers to continue to use water wisely.

The graph below shows the change in groundwater level over the last twenty four months compared to the Long Term Average (last 30 years).

<a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/ids-aug18.png"><img class="aligncenter size-full wp-image-7465" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2018/09/ids-aug18.png" alt="" width="1448" height="695" /></a>

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