A       Gas water pumps can be selected based on the desired application and how quickly the water needs to be pumped. GPM/PSI ratings, inlet/outlet size for water and hoses, how high you'll need to pump the water, referred to as Total Head Lift (measured in vertical feet), and how far you'll need to pump the water horizontally are the most significant elements in properly sizing a gas water pump. Finally, never use a gas water pump indoors since carbon monoxide will build up from the exhaust fumes, which can be fatal.