We are is Suffolk and the levels always drop in the spring and summer.
We have a couple of water butts we use to top the pond up, and only use tap
water in major drought times.
Evapouration will always reduce water levels, especially if it is sunny and
breezy.
When levels are low I have been known to rush out in a downpour to start
siphoning water into the pond so that the new water running off the roof
into the water butts doesn't get lost :-)

"James Cook"
inthisbityoushouldtypemynameseparatedbyadotwitha1 followingmysurname@btinter
net.com wrote in message ...
I've only got a small nature pond (surface area around 90 sq ft - deep
section around 3 1/2 foot), no moving water, no mechanical filtration. I'm
in the south east of the UK and we've had a fairly dry 8 weeks, we've had
a
hot few days (well, hot for here in April !) around 20-25 Celsius for the
last 3 days, its cooled off a bit today (12 degrees) and its gotten fairly
breezy overnight and today. I have noticed that the level has dropped
about
10mm in the last 24 hrs. Would you consider this normal ? I do have lots
of
grasses etc. growing on and invading the fringes of the pond if that makes
any difference.