Hydrogen can work as an energy carrier from multiple energy sources. Here is the conversion factors for 1 kg of hydrogen from a National Renewable Energy Lab document.
Hydrogen from coal: 7.6 kg of coal/kg hydrogen
Hydrogen from natural gas: 4.5 normal cubic meters/kg of hydrogen
Hydrogen from nuclear and hydro power: 58.8 kWh/kg of hydrogen
On average, about 3 gallons of water are needed to produce 1 kg of hydrogen
1 kg of hydrogen can potentially displace 4.35 kg or 1.58 gallons of gasoline
The document also has maps showing possible sources of Hydrogen. Below is Nuclear and Hydro.