Normally, any water you would drink is safe to use for an enema. Generally, faucet water is fine.
However, depending on your plumbing, hot water may contain trace amounts of heavy metals, primarily lead if you have copper plumbing.
This is because the higher temp has a tendency to dissolve the lead out of the solder joints on the way to the faucet. And there are also concerns that the faucet will contribute a trace of zinc, which is 30-40% of what brass faucets are made of.
And ........ believe it or not ........ in some old portions of some cities, there are places where lead pipe still exists.
Newer houses with copper plumbing have been required to use solder that contains antimony instead of lead ......... so generally this is not a problem. Depending on where you live, this has been required code for at least a decade or two.
There are so many variables as to heavy metal content, it can be a matter of degree as to the user's exposure.
My house has copper pipe with lead solder ......... going back to the 60's. One thing that comes into consideration is that the little bit of lead that actually comes in contact with the water eventually gets a skin of minerals and calcium on it over many long years, as does the inside of the copper pipe. I believe that the greatest concern was when the house was built, and these metals had an easier time of leaching out into the water. So I use warm water from the tap for my enemas. If this is the same as your situation, you'll have to make your own judgement.
And there is also the consideration that the water heater can contribute something .......... after all, water sits in these things for hours or days waiting to be used when you turn the hot water spigot.
And this is one of the reasons you are told to use only cold water to make coffee ........... because the slightest traces of metal or whatever can make a big difference in the flavor of the coffee.
You'll have to make your own decision, but in my case, I don't consider it a concern.