This study discusses the effects of water abstractions from two alternative sources
on the available water volume around Lake Naivasha, Kenya: the lake itself and a connected
aquifer. An estimation of the water abstraction pattern for the period 1999–2010 is made and
its effect on the available water volume in Lake Naivasha and its connected aquifer is
evaluated using a simple water balance modeling approach. This study shows that accurate
estimates of annual volume changes of Lake Naivasha can be made using a simple monthly
water balance approach that takes into account the exchange of water between the lake and
its connected aquifer. The amount of water that is used for irrigation in the area around Lake
Naivasha has a substantial adverse effect on the availability of water. Simulation results of
our simple water balance model suggests that abstractions from groundwater affect the lake
volume less than direct abstractions from the lake. Groundwater volumes, in contrast, are
much more affected by groundwater abstractions and therefore lead to much lower groundwater
levels. Moreover, when groundwater is used instead of surface water, evaporation
losses from the lake are potentially higher due to a larger lake surface area. If that would be
the case then the overall water availability in the area is more strongly affected by the
abstraction of groundwater than by the abstraction of surface water. Therefore water
managers should be cautious when using lake levels as the only indicator of water availability
for restricting water abstractions.