I replaced my hot water heater yestersday. There was little water pressure and today there is no water in the bathroom and kitchen sink. Can you tell my why this would be?
Thanks

Is there no water pressue for both the hot and cold water at the bathroom and kitchen? If so, it sounds like someone turned off the main water supply valve for the house when the work was done, and then forgot to turn it back on. If it's only the hot water that has no pressure, check that any valves at the hot water heater are turned on.

You may have knocked some crud loose which is now blocking the faucets. You need to shut the water off, remove the stems or cartridges, flush stuff out, and reassemble. Mot faucets dissemble by prying off a cap on the knob, removing the screw that holds the knob, and then the nut hidden by the knob. If that doesn't help, keep working back. Post back if you need more details.

What type of main valve do you have, a gate? Gates can fail when too fully/tightly closed. The gate can actually come off the end of the stem. I hate gates and would replace it anyway if that's what you have.