Salam Shaykh just wanted to say,
If someone suffers from OCD and they constantly get waswasa from shaytan regarding germs and bacteria and because of their negative thought processes they feel the constant need to wash their hands over and over again, what prophetic remedy from Quran and Sunnah would you give to someone and do they fall in the same category as someone wasting water which is a sin. Jazakum Allah
Salam, they certainly do not fall in to the category of someone who is wasting water for the simple reason that they are unwell.
In terms of remedy from the Sunnah, they need to seek protection from the shaytan by making dua and using duas based on the Qur’an and the Sunnah. Any good dua book would help you with that.
In addition, they should practice ignoring the whispers and obsessive tendencies by focusing on what is rationally sound. If it is rationally clear that they are clean, they should simply stop. The same principle would apply to people who have waswasah during wudhu. They must understand the rulings related to wudhu, fulfil that, and stop regardless of the suspicions. That requires them to become more process driven.
So, do the du’as and apply some logical and practical techniques. This may require someone to shadow them and help them stop according to the agreed process.