Do NOT do this. Hot water from the tap is a fantastic source of bacteria in your solution. Harm Reduction websites and graphics suggest this order of water use.
1. Bacteriostatic sterile water ampule, single use.
2. Boiled water, which is then cooled (low risk of bacteria).
3. Freshly run cold tap water (low risk of bacteria).
3. Hot water from tap (medium risk of bacteria).
4. Bottled water (medium risk of bacteria).
5. Part used ampule of water for injection (high risk of bacteria).
6. Toilet water (from the cistern, not the bowl) (high risk of bacteria).
7. Puddle water or saliva (high risk of bacteria).
Please do not suggest anyone use a water source that carries more risk of bacteria than boiling and cooling their water or using freshly run tap water. You do not need warm water to dissolve meth, if you are dissolving more stuff in it you are dissolving cutter into your solution, which is also not an ideal situation.