You prepare for what you expect. Best preparation is mental. How would I deal with _________? I expect to get use out of my investment in time, money and labor in regular use not only if society breaks down. So what fills in that blank tends to be something that has a decent chance of transpiring. I shoot for 2 weeks, Ice storms have taken out power in the area for that long. The folks that might have to go a month with blocked roads or floods cutting them off from town plan accordingly. I would imagine either because they think ahead or after the first month on short rations they would get smarter or move.
Un-scented non sudsing chlorine bleach is a cheap and effective water purification solution. Rotate through the laundry room if you still use bleach in laundry. Takes about a teaspoon per gallon. Some filter cloths are good too. https://www.doh.wa.gov/Emergencies/B...erPurification
I have a well pump but if I didn't have fuel for generator it would take about a 4 ft. deep hole in one low corner of the lot to dig a well that would produce some water. Hole flows at just past 3 ft.