بسم الله الرحمن الرحيم

The purpose of adding Dettol to water is to make it cleaner and purer.  If only one of the three qualities of Dettol (colour, smell, taste) becomes apparent in the water [after adding it to the water], then it will be correct to perform wudhu with it. However, if so much Dettol was added to the water that two or three of its qualities become apparent, then it would be incorrect to perform wudhu with it.