Is it permissible for a patient with influenza, who contracted it due to excessive use of water for scrupulosity (waswasa), to perform tayammum?

If the use of water causes illness, or increases it, or delays recovery, then it is permissible to perform tayammum until the patient recovers. After recovery, water must be used for purification. If the harm affects only washing certain limbs, then one must wash the limbs that are not harmed and perform tayammum for the rest. The same applies to ghusl from janabah. One must be careful not to be wasteful in the use of water.