Epoxy flooring is more of providing finishing and protection to the floor, but it is NOT anywhere near to waterproof due to the rigid nature of the coating. Waterproofing membrane is often very elastic and able to withstand a lot of pressure from ponding water. Some companies will offer you a non-hacking solution to simply re-grout your tiles and apply silane/siloxane water repellent and it is actually a temporary fix and won't be able to last long. My advice is if you are gonna stay in that house for long term, seek for a permanent fix that would last for decades, which requires hacking up the tiles for a complete waterproofing system and test.