What is the criterion of ‘fear’ of becoming ill if one uses water?
The criteria for the ‘fear’ of increase to ones illness or prolonging of their treatment or healing if they use water is firstly through apparent visible signs, secondly through one’s experience and thirdly from the advice of a pious Muslim doctor.
And Allah ﷻ knows the best
Imam Ahmad Rida Khan رحمة الله تعالى عليه
Translation by Dr Musharraf Hussain Al-Azhari Translator of Majestic Quran, www.majesticquran.co.uk