Most common places in a house is in the basement. Either on the wall closest to the street or in the furnace room. If on the front wall, it can be anywhere on the length of the wall probably 2 to 3...
If you have your own water heater there should be a shut off at the heater. If not I would look under the kitchen sink. There may be shut off valves at each fixture. If there is a central water...
Tubs usually do not have shut off valve for them. You have to shut off the main supply. Depending on how the house is plumbed, you may be able to shut the cold supply to the water heater and that...
Which water you talking about?
Under the kitchen sink there should be a C/W shut off If your talking toilet there should be a shut off left hand side under the tank.
Shower or bath tub possibly...