There are machines with an external water tank. For example, ECM Puristika, Belezza Bellona and Bellezza Francesca Leva (there may be others, but I have not come across them). When I was choosing a machine, it was a prerequisite. I didn't want a machine with an internal tank. And since there is very little choice among electric machines, the most likely candidate was Flair 58.

First of all, the pictures of the mentioned machines:







Now I will list the advantages of such a solution.

1. No harmful microfauna will breed in the water. We read here: "Many home espresso machines locate the water reservoir inside the casing; that's practical, but leads to the water being heated enough that a bacteria film will eventually form (of course, everyone empties and cleans the inboard reservoir regularly, right?)".
2. The airtight tank won't attract ants. People in FB groups noted that they found ants in the water because it is "ant heaven" - warm and humid! But to detect these ants, you had to open the lid and look inside. Every day! If ants are found, you have to take the tank out of the machine to pour out the water, and in many expensive prosumer machines, this is a below average pleasure. That's the main reason I wanted an external tank - ants loved to use the built-in tank of my previous machine as a swimming pool. We invited an ant exterminator several times, but he couldn't do anything. The ants only completely disappeared when I sold the espresso machine (this happened in October 2020, when I got rid of my caffeine addiction; now I'm back to my favorite hobby with decaf only).
3. You can clearly see when the water runs out and it's time to refill. This can also be seen on some machines with an internal reservoir, but not all. For example, my previous machine just stopped working when I forgot to refill the water. I was making a shot, and all of a sudden - boom! - there's a ristretto in the cup!
4. Flexibility in terms of location. If the surface is deep, and it is necessary to arrange a lot of devices along the length, then hide the tank behind the machine. If, on the contrary, there is enough space on the length, but the depth is limited, then put the tank on the left or right of the machine. And if there is not enough space in all directions, then put the tank behind the grinder, which, anyway, already takes up space wide (but not deep).
5. It's not a practical advantage, but... the machine with the external tank looks so cool! The picture doesn't convey it, but in real life this setup with hoses looks like the equipment of a serious coffee drinker, or like... a medieval alchemist's lab! It's fascinating! Aesthetic appeal enhances mood, which means that it is also a practical advantage.
   
   

However, there is a disadvantage with the external tank too - after all, it is a glass vessel, you need to be careful and cautious. Don't buy it if you have a cat, ha-ha!

Of course, the best solution is to connect the machine to the water supply, but not everyone has such an opportunity.