Showers and tubs do not usually have shut off valves on the supply lines. To shut the water off you will have to shut off the main water line. There should be one on the cold water line to the water heater. This may shut both the hot and cold off or just the hot. There will be one in the main line coming into the house on the basement wall closest to the street or at the water meter.
The valve in the shower control needs to be renewed.
It will not work to smoke while in shower as the water will turn off the cigarette or cigar.
Usually clogged shower heads. Turn water off and shower off. Screw shower nozzle off by hand or with pipe wrench. Turn water and shower on with nozzle head off if water flows clean or replace nozzle. If water pressure is still too low with nozzle off check shut off valve and open valve more. Make sure main water shut off for your house is open enough to allow adequate water pressure.
yes you are even though you are not in the shower you are still wasting water
Does the shower drip constantly over a period of 4-5 hours, if not, it's water holding in the shower head which has a water saving feature that holds water in the head. If it drips constantly, you'll need to change your seals on your stems. It's fairly simple if you have the correct tools.
SWAG
you have trash in your line take the shower head off and remove trash or possibly in water valve at shower
You need to check your hot/cold handles or the shower spicket. Not sure what type you have, but they come off. More than likely you need to just replace a gasket..
to rinse the chlorine off their bodies.
Employ a plumber.
The valve is not be diverting all the water. This valve may need to be replaced.
we can save water by turning off the Fauset and taking a short shower.