Hi on-a-mission, you can often find distilled water in gallon size in supermarkets, and frequently in pharmacies, although they usually charge more for the same thing. I have often just used warmed bottled spring water because spring water typically includes essential minerals.
When I do juice fasts I usually give myself a saline solution enema every day. Most days while fasting it's something I look forward to. If I have any hint of a headache it's usually gone before I finish on the toilet. It also tends to suppress my appetite, and if I had a bad taste in my mouth it usually subsides or disappears altogether.
You can do the enema whenever convenient. Some people prefer before bedtime, others first thing in the morning, or perhaps mid-day. The time of day doesn't really matter.
You can go to the following links for more information how to go about it: