Assalaamu alaykum. There is a place near the toilet bowl in my washroom where the water never dries. A few days after moving in, I noticed a bluish colour in the water and thought that the toilet might be leaking as the soap in the water makes the water in the toilet bowl blue. Later on, I realized that some of the stains might have been dust, which clumps together, and since I cannot remember whether I was wearing my glasses or not, I cannot tell if the water was really blue or just had greyish dust clumps. After calling the maintenance technician, he told me that the water sits there because the tile in that area is slightly depressed, but he seemed not quite sure and offered to rework the bathroom. I feel scared that the water is impure and that my prayers might not be accepted because of it. Should I have them change the tiles just to make sure there are no impurities and the toilet is not leaking?
Secondly, when I was far from Islam, I used to think of things like whether the false pagan deities of Ancient Greece were actually jinns that the people worshipped and if the war in their stories of Titans and the deities was a warped version of the war between angels and jinns. Do these thoughts constitute apostasy?
Thank you.

All perfect praise be to Allah, the Lord of the worlds. I testify that there is none worthy of worship except Allah and that Muhammad is His slave and Messenger.

As for your first question, you do not have to change the bathroom tiles, and in principle, this water is pure, unless you are certain that it is impure to such an extent that you can swear that it is impure. Your previous prayers are valid in any case.

As for your second question, you did not do something that constitutes apostasy, though those beliefs were false.

Finally, we draw your attention to the fact that Waswaas (devilish whisperings/obsessive doubts) are a great evil, so you have to deal with them and get rid of them, because getting carried away with them leads you to a great evil.

Allah knows best.