Serving parts of North West London and the Home Counties.

Groundwater levels

Central Region


Central region water levels hydrograph

*The long term average (LTA) has been calculated statistically, using the long term data record for this hydrograph. The respective drought zones are used as operational triggers, and have been derived using the LTA.


Groundwater levels in our Central region remain in drought zone 2, below the level that they were at this point in 2017 and 2018. Despite receiving above average rainfall in December and March, this winter has been dry, with April rainfall being 25% of the LTA. From October to April inclusive (the recharge period), rainfall has been 82% of the LTA. The period has been characterised by periods of settled conditions and above average temperatures. As such, soil moisture deficit (SMD) finished April above the LTA and the proportion of rainfall likely to contribute to Chalk groundwater recharge has been low. The high SMD decreases the recharge component from rainfall, as more water is absorbed by the soil. This is likely to indicate the end of significant Chalk recharge this spring, unless exceptional rain falls, akin to the spring of 2012.

Chalk groundwater levels in our Central region have declined since mid-April and this is likely to continue until the autumn if we receive 120% or less of the LTA rainfall, remaining in drought zone 2 for this period. A rainfall pattern of approximately 100% of the LTA could potentially see groundwater levels approaching drought zone 3 in late autumn 2019, while under a 60% LTA scenario we would likely approach drought zone 3 in late summer, with levels lower than those observed during the recession period of 2017.