They are currently going round cleaning the pools one by one. They seem to have done a good job on the pool outside block 3/4. It is part of the program to spruce up the complex which includes the waterproofing work on the stairways (hence the scaffholding) and eventually the repainting of all blocks.
Don't worry too much about the missing water in the pool. Ok the weather is mild and even warm at times but the water is still freezing and will be for a while yet, until we get to summer, only the brave/stupid would be in there in April!