At sea level, 1 liter of water weighs 1 kilogram. At higher temperatures, there are fewer water molecules in a given volume and water is less dense, so 1 liter of water weighs slightly less than 1 kilogram.
Having substrates or salt in the water also influences the weight of water. The mass of the substrate determines how much the water's weight is increased. Since water dissolves more substances than any other liquid, having other compounds suspended in water is common. The molar mass of water is calculated by adding the molar mass of one oxygen and two hydrogen atoms. The molar mass of oxygen is 16 grams, and the molar mass of hydrogen is 1.008 grams. Calculating 16 + 2(1.008) gives water's molar mass of 18.016 grams.