Andy BB
Although you are correct, and doing it this way means you can take on water that is not potable, it is called 'rectal infusion' and not an enema.
If you think about it, having an enema would be defeating the object, and would dehydrate you (plus make you look a bit kinky lol).
All kinds of water can be taken on board with rectal infusion, as to be honest, its not going to a particularly clean area of the body, so crystal clear is not needed.
I remember watching a special forces soldier demonstrate rectal infusion with a warm cup of tea. About one second after the cold tea entered his bowel, he screamed out 'bloody hell that's vile'
We asked if it was burning, and he replied......... 'There's no bloody sugar in it!!'
OK the last bit was made up, but I couldn't resist it lol.
I don't know which temperature would hydrate you the quickest, but depending on how you dehydrated, electrolyte in the water would be a massive help. Water is also at its most dense at 4 degrees C, so at this temp you would end up with more volume of water in you once it warmed up. If you have no precise control of the waters temperature, but can get it warm, adding a mint leaf will also speed up water absorption.
One last thing on rectal infusion (true this time), is that red wines will burn your rectum, as can fizzy drinks.