Hi Nick - I make americanos 95% of the time. As img says - you shouldn’t make the drink by putting more and more water through the puck as the continued extraction would normally make a bitter and not very nice drink. For americano I often make a 1:2.5 or 1:3 ratio espresso as the base - don’t be afraid to go over 1:2 as u have a lot more freedom when u know you’ll be adding more water anyway. In terms of adding the extra water - a standard kettle is fine imo. The water does not need to be temperature controlled as brewing is already done and as I learnt on these forums, you cannot burn an already brewed espresso with very hot water. I do use the hot water tap on my dual boiler espresso machine though my machine is plumbed in so don’t worry about tank refills plus I do it often enough to ensure fresh water is in there.