I hope you've been doing it annually or at least a few times since installation. If not, you may have shaved years off of the life of your water heater. Let me tell you about my wonderful experience...
My water heater is 7 years old and has never been drained in it's life. I started noticing a brown tinge to the water before drawing a bath for my son. Wasn't sure what the deal was but I spent the better half of an hour filling pot & pans, warming them on stove and lugging them upstairs to fill it with water I trusted. Ugh, what a process. Really makes you appreciate modern conveniences like hot tap water.
Quickly I learned that if it had something to do with city water then my cold water would be discolored. If it had something to do with my water heater, only my hot water would be discolored. Lucky us.
Several You Tube videos later my husband and I felt confident enough to give draining our water heater a try. We hoped that we would expel any sediment and be back to normal. Yeah, we may need to be replacing ours soon. Notes to self include;
- Be sure to shut the cold water supply valve FIRST & keep it off until it's drained
- Leave all hot water faucets open until finished (or you'll be sorry)
- Introduce air into system to push existing water out of drain spigot (usually by adjusting a pressure-relief valve)
- Extend a garden house outside instead of using buckets is a great idea
- When water is turned back on, filters on every faucet may have to be taken off and cleaned to remove sediment
- Helpful Video and Bob Vila's Instructions.
Oh and close the drain valve BEFORE removing the garden hose!
Long story short: if the water is still brown after 3 or 4 five gallon buckets and hot water seems to run out a little faster than it used to, it's probably time to replace it. They can cost anywhere from $400 to $2500 depending on type and size. If you willing to spend a little more for a lot less maintenance, Rinnai manufactures the #1 selling tankless water heater.