It rained everyday in Narobi, 6 days in all, as well as Mara Plains which was practically flooded, Lewa Wilderness and Borano so there actually is water.
Kenya has two rainy seasons, which normally occur naturally, and, yes there was exceptionally heavy rainfall in the Mara this December. BUT .... Kenya has made the headlines in the last few months because of drought - along with Ethiopia and Sudan.
Water is a precious resource in Kenya. The number of people who risk bilharzia and being eaten by crocs and hippos because they have no running water and use nearby lakes or rivers is higher than you might ever believe 4halex. I know this from personal experience. Just because it rains twice a year does not mean that there is enough for the rest of the year.
Again, from what you've posted, having spent so much on your trip, it seems that you are still far from aware of real life in Kenya. Sometimes however a point needs to be made more than once or even more than ten times because communication doesn't flow between the person giving it and the person receiving it ... which may have happened to guests who had stayed before you, hence the manager having to 'rub it in'.
We all have to be aware of different standards of living and natural resources when we travel - and hopefully that knowledge and our experiences make us better travellers.