In Mexico City, water from the tap is not fit for consumption. You don't even use it to make your coffee or boil your vegetables -water in this city has a slightly foul smell, reminiscent of ancient decaying swamps and natural gas.
And to make the taste even worse, it's also heavily chlorinated.
You buy jugs of spring water in the shops -a heavy haul- or have a company deliver the water to your home -also a drawback, as they will not deliver anything if there's nobody home.