In the absence of a consensus from experts the answer is: probably. Tap water in Cairo is unlikely to cause acute illness, but in the long term it’s probably healthier not to regularly drink it without filtration.
In this article Isabel Esterman assesses the quality of the drinking water available in Cairo. What is the status of water when it leaves the treatment plant and when it finally comes out of the tap? The analysis is then followed by practical suggestions on what households should do.