It is good to have small (6 Gallon Jugs) because you can move it – load it into a vehicle. You can not move a large tank easily.I live in a city with no rivers or natural water nearby. I cleaned my 750 liter (198 Gallon) tank yesterday and filled it with ‘clean’ drinking water (not filtered). This large amount would be able to help us for quite a few days, depend on how much we use.
Worse case 12 liters per day = 3 Gallon (drinking humans & animals, cooking) That means maybe 2 months supply only?
Otherwise 2 – 3 weeks. (drinking, cooking, bathing, washing clothes, watering more plants & animals) And maybe use old bath water to flush toilets if you know when you will get more (rainy season)
I think it is important to have at least one other tank to collect rain water permanently. You can not afford to put not that clean water in a big tank – it takes a lot of water to clean a tank. If you rely on only the big tank of water for drinking and it becomes unhealthy to drink it, is a big loss. Especially if you not have the means to treat it.
I try to stock up on regular Jik (not perfumed bleach), Milton and already mixed powder treatment sachets that is lighter to carry. Got a 2500 Liter tank (660 Gallon) with borehole on another property where it might be safer for a while.