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.
<h2>Rainfall at Havant</h2>
The Rainfall Records at the Company’s Head Office at Havant date back to 1886.

The month of February saw way above average rainfall with approximately 190% of the LTA (Long Term Average) rain for the month.  Rain fell on 72% of the days, with the maximum daily rainfall approximately 15.5mm on 15 February 2020.

Total rainfall for the month was 111.7mm, greater than the 30 year long term average of 58.81mm.

<a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/dailyhav-feb2020.png"><img class="aligncenter size-full wp-image-9562" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/dailyhav-feb2020.png" alt="" width="1179" height="564" /></a><a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/ltahav-feb2020.png"><img class="aligncenter size-full wp-image-9563" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/ltahav-feb2020.png" alt="" width="1179" height="564" /></a>
<h2>Groundwater Levels at Idsworth</h2>
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.

Ground water levels have continued to rise at rapid rate during February due to the above average rainfall that has been experience over the last six months. At the end of the February levels were 5.81m above the LTA of 25.24m and are “high” for this time of year being 2.74m above “normal” levels at 31.05m.

So long as rainfall continues to remain close to average, 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 LTA (last 30 years).

<a href="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/ids-feb2020.png"><img class="aligncenter size-full wp-image-9564" src="https://www.portsmouthwater.co.uk/wp-content/uploads/2020/03/ids-feb2020.png" alt="" width="1181" height="565" /></a>

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