Gas for cooking and maybe hot water means a propane cylinder. The most common size for a house is a 25 lb. cylinder but there are also 35 lb. and 100 lb. cylinders available.
The two big vendors are Tropigas and Zeta Gas. The way it works is you buy a cylinder (or two if you are the kind of person who doesn’t want to run out of gas in the middle of cooking dinner) and then “trade them” for a full cylinder. Some of the gas distributors sell cylinders — otherwise you will find them in hardware stores and places that sell stoves.
For a 25 lb. cylinder, expect to pay between Q250 and Q300. You will find places that trade empty for full cylinders all over the place (even some tiendas have them). The cost for a refill varies depending on the current price of gas. I have paid as little as Q90 but right now the price is Q120. Generally the sellers will deliver, typically on a bicycle.
Most people don’t drink tap water — a good choice. You have two decent options. The first is to purchase 5 gallon “bottles” of water which is called a garafon. The typical cost is Q8, delivered much like gas cylinders and sometimes by the same people.
The second option is to buy a decent water filter. Locally you will find ceramic filters in hardware stores. Basically it is a plastic or glazed ceramic container with an un-glazed ceramic filter inside. How well they work is not clear to me.
The other choice is to buy a filter with cartridges you replace. I have used Berkey filters for decades. They are initially expensive but a set of filters will filter thousands of gallons. You will find information about how effective they are on their web site.