Hot water only lasting 10 minutes - Rheem 50 GAL ELEC TALL Water Heater 6YR SC 83VR522

SOURCE: Rheem 49 gal model 81V400B

Ordinary tank-type electric water heaters are fully repairable by homeowner.

A) Basic info on Rheem
Rheem electric water heater website:
http://www.rheem.com/products/tank_water_heaters/electric_water_heaters/
Find age of Rheem: look 2nd and 3rd digit of serial number, for example 06 is 2006

B) Water heater has some hot water.
That says certain things: upper element is working, water heater electricity is working, reset button is not tripped, and heater is not experiencing run-away overheating event.
http://waterheatertimer.org/How-it-works.html

C) That leaves 4 suspects that cause lower amount of hot water.

1) TP valve is running hot water out of tank -or- leaking faucet is running hot water out of tank.
Check for leaks
http://waterheatertimer.org/How-to-replace-TP-valve.html

2) Lower element is burned out.
Test lower element using inexpensive multi-meter from Home Depot.
http://waterheatertimer.org/How-to-test-water-heater-element.html
Replace element with same wattage shown on label, and clean out sediment:
http://waterheatertimer.org/How-to-clean-sediment-out-of-electric-water-heater.html
http://waterheatertimer.org/Clean-sediment-out-of-water-heater.html

2) Upper or lower thermostat is bad.
Replace both thermostats for about $25.
http://waterheatertimer.org/How-to-replace-thermostat-on-electric-water-heater.html

3) Burned or shorted wire located between upper and lower sections of tank.
Turn off power. Open covers on side of tank. Remove insulation. Inspect parts for signs of high heat and burning. Especially check lower element. Tighten any loose wires. Replace part that shows signs of burning.
Put insulation and cover back over thermostats so cooler outside temperature doesn't cause thermostat to misread tank temperature.
http://waterheatertimer.org/How-to-troubleshoot-electric-problems-with-water-heater.html

Add a comment for more free help.
Also take advantage of fixya phone service.
For a price, expert speaks with you over phone while you work on water heater or any do-it-yourself project.
Fixya is always less expensive than a service call.