What is Tallah Tank, you might ask. It’s allegedly the world’s largest water tank of its kind, holding a whopping nine million gallons of water to supply a city burgeoning with over 15 million people. If Tallah were to store aviation fuel in its belly, writes The Telegraph newspaper, it would be enough to fuel 158 jumbo jets.

It’s a landmark in my native Kolkata that very few tourists ever see. Located in the northern part of the city, Tallah is hardly a destination. But it’s a marvel in a city where very few things work efficiently.

“In fact,” a local Kolkata Municipal Corporation official told The Telgraph, “the city would run dry of the tank were to be shut down for a day.

Tallah has never let Kolkatans down. It has sprung only 14 leaks since it was built in the days of colonialism. The British Empire crumbled (thankfully) but Tallah kept standing. Massive. Majestic. Even menacing.

That’s how I looked at Tallah as a little girl who passed it by in a taxi on the way home to Baranagar from New Alipur, in the southern half of the city.

After a long ride through congested streets and snaking lanes, Tallah was my sign that home was near. Once the rickety black and yellow Ambassador whizzed by the tank on Barackpur Trunk Road, I could see the tops of coconut palms and the muli-story buildings of the Indian Statistical Institute.

I didn’t know then that Tallah was Kolkata’s source of water. But it was appropriate that it was such a vital symbol for me.

Happy 100th, Tallah.