How much water to store for emergency?

You're not overthinking it, it's the bit most people skip. The 3 litres a day is mainly for drinking and basic food prep. For everything else: if a storm or a supply problem is forecast, fill the bath and a few large pans, as that water is fine for flushing and washing. Pouring a bucket of water straight into the bowl flushes the loo without needing the cistern. And in longer outages, water companies usually set up bottled water stations and deliver to people on their Priority Services Register, so it's worth signing up if that applies to you.

Hand sanitiser would be ok for short-medium term hygiene purposes, with wipes as a back-up. Dry shampoo works well, too, but to be honest I think that if people are holed up in a power cut they probably won't care too much about what they look like.

Clean hands matter, obviously, so large bottles of sanitiser seem a sensible option.

If there is not enough water to flush the loo, you can line it with heavy duty garden waste bags, cover with a scoop of cat litter after each use, then tie the bag and put in the outside bin until collections resume. I posted this on a different thread, but people may not have seen it. (wee in a bottle, and dispose of that separately).

Google says that water is safe to drink after the sell-by date, but may not taste as good, because of plastic leakage, but that as this is food grade there will be no harm done. Better a slightly plastic-tasting drink (you can always disguise it with a bit of squash) than gong thirsty, I think.

I certainly don't drink 3 litres a day, but can imagine needing at least that if toothbrushing/cooking (assuming we can cook) is taken into account. Maybe not 6 litres between us though, as we'd obviously cook two portions at once.

Oreo

I had to ask a man to move his trolley in the supermarket this morning, it was blocking the aisle as he was hefting huge packs of bottled water into it, the whole trolley was taken up with bottled water and nothing else.Could have been a sensible reason for this behaviour or he could have been a prepper.
Has it started already😱
I must remind people that bottled water does have a date on it and as for hygiene wipes, they dry out after a while.

Oreo, Ive found that if packets of hygiene wipes are kept inside a plastic bag, they will stay moist for quite a long time, even after the packet has been opened.

I had to ask a man to move his trolley in the supermarket this morning, it was blocking the aisle as he was hefting huge packs of bottled water into it, the whole trolley was taken up with bottled water and nothing else.Could have been a sensible reason for this behaviour or he could have been a prepper.
Has it started already😱
I must remind people that bottled water does have a date on it and as for hygiene wipes, they dry out after a while.

Oldnproud

Consider getting a few packs of body wipes for cleaning of self - and a few packs anti-bacterial for certain other types of cleansing, too. Thy take up a lot less space than bottles of water.

We have had to do that more than once.
In Spain in the motohome where because of water shortages the water stand pipes are turned off.
The same on the French canals and rivers.

Consider getting a few packs of body wipes for cleaning of self - and a few packs anti-bacterial for certain other types of cleansing, too. Thy take up a lot less space than bottles of water.

You will need it to drink, boil, wash, cook and most importantly to flush the loo, although the water in our water butt could be saved for that.