Reciting Quran over water for ruqyah and heating it because the weather is cold
Question

I am a young Muslim man who has been affected by some kind of sihr (witchcraft). With regard to ruqyah by reciting Quran, can I recite the Quranic verses myself over the water? Do I have to remove all my clothes when doing ghusl? And finally, is it permissible to heat the water because the weather is cold?.
Praise be to Allah.Firstly: 
We ask Allah to heal you, make you well and divert away from you that which you are experiencing. 
Secondly: 
It is permissible for you to recite Quran over water and to drink some of it and wash yourself with it. This has been discussed and what should be recited to cure spells has been mentioned in the answer to question no. 12918. 
With regard to what you mention about reading for yourself over water; in Saheeh al-Bukhaari (5735) and Saheeh Muslim (2192) it is narrated from ‘Aa’ishah (may Allah be pleased with her) that the Prophet (peace and blessings of Allah be upon him) blew over himself and recited al-Mi’wadhatayn during his final sickness. When his pain got worse, I would recite over him and wipe his hand over him, seeking its blessing. 
Mu’ammar said: I asked al-Zuhri how he used to blow over himself. He said: He used to blow into his hands then wipe them over his face.  
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: The words “in his final sickness” do not mean it is limited to that, rather ‘Aa’ishah indicated that this happened at the end of his life and that it was not abrogated. End quote. 
Thirdly: 
It is not essential to remove all one’s clothes when doing ghusl, whether it is ghusl for ruqyah or to cleanse oneself from janaabah and so on. What matters is that the water should reach the skin. 
‘Uthmaan (may Allah be pleased with him) would do ghusl without taking off his clothes, because of his deep modesty (may Allah be pleased with him). Narrated by Ahmad (543) with a hasan isnaad. 
In Kitaab al-Ghusl of his Saheeh, Imam al-Bukhaari included a chapter entitled: One who does ghusl naked when he is alone and in seclusion, but whoever can cover himself, covering is better. Bahz ibn Hakeem narrated from his father, from his grandfather, from the Prophet (peace and blessings of Allah be upon him) that Allah is more deserving that we be modest before Him than other people. 
Al-Haafiz Ibn Hajar (may Allah have mercy on him) said: When he said it is better, this means that it is permissible to wash oneself when naked, and this is the view of the majority of scholars. End quote. 
There is nothing wrong with heating the water and reciting over it. 
And Allah knows best.