Effect of water occurrences on methane adsorption capacity of coal: A comparison between bituminous coal and anthracite coal

•Adsorbed water negatively impacts CH4 adsorption for both anthracite and bituminous coal.•Adding non-adsorption water can reduce adsorption capacity of anthracite coal but not bituminous coal.•Negative impact of non-adsorption water on gas adsorption in anthracite coal are related to both the hydrophobicity and pore Jiamin effect.•Well-soaking during hydro-fracturing is necessary for anthracite coal reservoir.•Well-soaking during hydro-fracturing is unnecessary for bituminous coal reservoir.