"Kevin G." wrote in message
oups.com...
My 30-year-old 80-gallon electric water heater has begun to not work
very well. When taking a shower, after about five (5) minutes, the
water begins to lose its heat, and I have to turn the cold water
almost completely off in order for the water to remain warm.

Good possibility the dip tube inside is broken. After 30 years, time for a
new heater as you are on borrowed time.