The tanker arrived before the sun did. I remember lying in bed in Madras, maybe eight years old, listening for that particular rumble on the street outside, a diesel engine and a slosh of water in a metal belly, and knowing that in a few minutes I would be standing in a line of steel drums and plastic buckets while my father worked out how many liters we needed to get through the next twenty four hours.

That was the real arithmetic of my childhood mornings. Not multiplication tables. Water.

For bathing, luxury meant half a bucket of tap water heated in a vessel on the gas stove, then carried to the bathroom like something breakable. Every mug you poured over your shoulders had already been accounted for somewhere in my mother's head. You did not daydream under that water. You used it, mug by mug, and you knew when you were done.

A bucket holds a fixed amount. You can see the bottom of it. Nothing about a bucket lets you forget what you are using.

Decades later I split my time between Hyderabad and the United States, and the tanker's rumble has mostly gone quiet, replaced by overhead tanks and electric geysers that never run cold. Still, in Hyderabad flats with modern plumbing and constant running water, I keep finding the plastic bucket and mug sitting under the shower head, untouched, while the family bathes exactly the way I did as a boy.

For years I assumed this was pure habit, something inherited and never questioned. Now I think of it as an engineering decision made by hand. A standard shower head releases somewhere around ten to fifteen liters of water a minute, more with generous pressure, and it does this without asking you to notice a thing. The bucket asks you to notice.

The numbers, when I finally looked them up, surprised me less than I expected. Domestic water use in the United States runs somewhere around 300 liters per person each day. In urban India, the commonly cited figure is closer to 135 to 150 liters, and that number includes plenty of households with a shower head bolted to the wall who reach for the bucket anyway. Multiply either figure by a billion or more people and you start to see why water planners treat India and the United States as two different water countries sharing one planet.

The planet itself is not as generous as it looks from a plane window. Of all the water on Earth, about 2.5 percent is fresh. Most of that is locked in glaciers and polar ice or sitting too deep underground to reach. What is left, the water actually running through rivers and lakes and shallow aquifers, the water a tap can reach, comes to well under one percent of everything Earth holds. I did not know that number as a child standing in line for the tanker. I only knew that water ran out, and that the running out was personal, mine, ours, measured in drums and mugs rather than percentages.

Now when I travel and step into a hotel shower where hot water arrives instantly and keeps arriving for as long as I let it, I still feel that flicker, the boy in Madras doing math in his head before he has even picked up the soap. It does not ruin the shower. It just means I know exactly what I am standing under.