What is the mass of milliliter of pure water? What about 1 L of water?

Yes, at 3.98 °C one milliliter (cubic centimeter) of water has a mass of 1.00 gram If the water is pure, and the temperature and pressure are both at standard values, then the mass of one milliliter of water is 1 gram.

kinda 1 milliliter (ml) of water weighs 1 gram (g). The prefix in front of the unit tells you how to move the decimal. 1 milliliter = 0.001 liters because "milli" means "thousandth". 1 "thousandth" of a liter = 0.001 liters.