G'day Harro.
That's a lot of Bundy!
Kilo = thousand
Mega = million
One cubic meter of water is one thousand litres (one kilolitre) and very close to one thousand kilograms.
Therefore, if you have a pool that's 50m X 25m X 2m (guessing at the olympic size), you'd be looking at 2.5 megalitres.
Cheers, Slates
(I hope I've got that right!)