I'm curious what a realistic estimate of service loss even is. We had pretty close to this happen three years ago in Texas and only had about two hours of electricity a day for two weeks. That was more than enough to make it barely a disaster, even though we lost all vehicular services and could not shop or receive deliveries for that entire time. We still had water service, which does not seem to universally rely upon long-range electrical grids being consistently up.
Simply surviving something like this, provided you can rely on the grid coming back eventually, is mostly just hunkering down. The water requirements here are referring to what is needed to sustain activity. I was also a logistics officer for a combined arms battalion and the water needs of an infantryman fighting a war are quite a bit greater than a family hunkering down in their house. Drink whatever non-perishable liquid you have, slowly, and it will take at least a week before you dehydrate. If you're not already anorexic or some kind of extreme endurance athlete, it's going to take most people at least a month to starve. You won't have a pleasant existence, but as long as you stay in place and don't try to do anything, you can easily stay alive without much.
If you're talking true Walking Dead level post-apocalypse LARPing civilization is gone and not coming back, stored supplies do nothing but delay the inevitable. You need to learn how to live off the land and probably fight for it. Look at people taking shits in the street that Hacker News hates so much and see what they do to survive without working utilities and access to grocery stores. Eat trash. Drink rainwater. Stay out of sight as much as possible and look insane and dangerous when you're not out of sight.