From density, it can be said that 1 g of water has volume of 1 ml.
Thus, 1.8 ml of water has mass of 1.8 g.
1 mole of water weighs 18 g.
Thus, 1.8 g of water corresponds to 0.1 mole.
1 mole of water contains 6.023×1023 molecules.
Hence, 0.1 mole of water will contain 6.023×1022 molecules.