بسم الله الرحمن الرحيم
If water is not available within one mile then you should join the salah by doing tayammum. However, janazah salah shall not be valid without wudhu if you are able to do wudhu, but if you are not able to do wudhu then Janazah salah shall not be valid without tayammum.
If in case of doing wudhu there is possibility that janazah salah shall be missed then it is lawful to do tayammum for janazah salah though water is available. [N]
Allah knows Best!
Darul Uloom Deoband
This answer was collected from the official ifta website of Darul Uloom Deoband in India.