Re: which weighs more HOT water or COLD water.

That depends on how you are weighing the water. Between 4°C (39.2°F) and 100°C (212°F) water expands slightly as it is heated, such that hotter water is less dense than colder water. This means that a given volume of hot water will have slightly less mass, and therefore weigh slightly less, than an equal volume of cold water. However, changing the temperature of water does not change its mass (ignoring evaporation), so a cold glass of water will weigh the same after it is heated up, because the mass is the same, although the volume has probably changes slightly. I guess the moral is that volume is not a reliable measure of "amount", since different amounts (masses) of the same thing (water) can occupy different volumes depending on how hot or cold they are.