As recommended by other users, I use Brita filtered water in my Gaggia Classic espresso machine. Brita sternly warns against using such water for longer than one day. This might be fine when keeping a family supplied with coffee, not so much when it’s just for one. It’s wasteful in terms of water, and also in terms of filter use, as it reaches its throw-way date long before it’s processed the optimum amount of water.
I get through, at most, 3 200ml mugs of café crema a day (think of an Americano, but 100% coffee, no hot water), and often just one cup.