Water. We don't think about it much, but we absolutely need it to survive. And to be healthy, we need clean water. When we lived in America, we took clean water for granted. We turned on the tap, and there it was. Unless there was something drastic, like a hurricane, it was reliably available, even when the power was out. We washed in it. Did our dishes in it. And drank as much as we wanted. It's not that way in much of the world, even in a fairly modern city like Chiang Mai. The water in our neighborhood is fairly reliable, but we still have a holding tank for those times when there is no water.
And the water isn't really that clean, so we have these water filters to help clean it out some. See that center water filter? It's usually filthy within 2 days of being cleaned. These guys help make the water clean enough to bath in and wash our dishes with (so long as we crank up the heat on our water heater).
But we still don't drink the water; not even the locals do that. So our drinkable water is delivered to the house every other Tuesday in these large, plastic bottles. We get 6 at a time, and that's about right for our family. We have a mechanical device for pouring the water out, as well as a traditional water cooler/heater. It's a pain to haul these heavy guys around, but we're grateful to have clean water that we don't have to boil before we drink or cook with.