I use a heat gun, but possible to use a good hair dryer also. Ive fixed some pretty messed up bumpers. Dont know how hot water works...seems a little hard to buy that. Dont always believe stuff you see fixed on YouTube. I dont know how many headlights ive had to REfix or replace because someone tried a method seen on YouTube. One tried a drill and WD40 on his Mercedes. I had to replace that $1000 set of headlites. He melted big gouges in them.