In human cell how many number of water molecules can be there?

Answer 1

Let's go with an ovum, which is the largest cell in a human body: http://en.wikipedia.org/wiki/Ovum

At 145 um diameter, its volume is 1.5963E-6 cm^3. Assume it's 90% water, use density of water to figure out total mass. Use atomic mass in grams to figure out number of moles. Multiply that by Avogadro's number to get number of molecules.