It depends on how much water comes out of your shower head.
1 gallon
depends on how much you want, like i have 700 gallons.
Because to fill up a bath you need to use a lot of water, this water is more then what a typical person would use to shower (showers use less water/min then filling up the bathtube)
millions of gallons of water
1/4 GAL
A shower head would use between 60 to 75 gallons for a 30 minute shower.
I have made it before and you can do it by hand but it is much easier to use a mixer.
You can make the whole shower experience a game. For example, who can get to the shower first, use the water toy guns to play a shooting game with your child. Use dye to dye the water in the water gun. Tell your child he will get a treat at the end if he/she behaves in the shower.
Some ways to use less water are, turn off the water when you brush your teeth, take a bath instead of a shower, and do not run to much water when you do take a bath!
It depends on the shower heads, bath heads, and the person. If you take a long shower, and use little water for a bath, bath is better. If you use a lot of water for a bath and take short showers with water saving heads, a shower would be better.
switch off lights when your not using them only boil as much water that you need don't use too much water in the shower switch off the PC when not in use