No country currently backs its currency with gold, but many have in the past, including the U.S.; for half a century beginning in 1879, Americans could trade in $20.67 for an ounce of gold. The country effectively abandoned the gold standard in 1933, and completely severed the link between the dollar and gold in 1971.
It seems like a sensible provision, but business is business and the law does not prevent charging for the use of a glass or for service. It doesn’t extend to filtered tap water. They can charge for that. But if they serve alcohol, they have to provide free drinking water, whether it’s filtered or unfiltered.
All communication between Mars and Earth goes through satellites. Because of the distance, there is a substantial delay. As communication signals travel at the speed of light, this means that it can take between 3 and 22 minutes for the information to reach the other end, so a phone call would not be practical.