Thanks everyone who has replied to this thread. Based on the
suggestions here, I have formulate this plan:

I have asked my neighbors. Seem like the waterheaters around here last
a long time (something like 10 years). This means I don't need to be
in a hurry to check the anode rod. I can afford to wait until the
coming summer when we don't expect to use hot water that often.

Meanwhile, I will do these:

- Use a union-joint to extend the drip pipe from the relief valve to
no more than 6" above the floor. That union-joint can be taken down in
case I need to replace the relief valve.

- Add a flood-alarm near the bottom of the waterheater ... just in
case the waterheater cannot wait for the summer.

In the summer next year, I will do these:

- Replace the ball-valve in the cold water supply that cannot
completely shut off. Seem like the plumbler used too much heat when he
soldered the ball-valve to the copper pipe that melted the plastic
seal inside the ball valve. I will replace it with a ball-valve that
uses compression fitting.

- Replace the rigid connections at the water pipes and gas pipe with
flexible connections.

- Examine the anode rod by pulling it out as much as the headroom
allows. I probably need to use WD-40 to loosen the rusted connection.

- Replace the anode rod with a flexible version if the anode rod is
almost a goner. Preferably a magnesium version. I will contact the
manufacturer of the waterheater to see if they sell it. Wrap 3/4 of
the threaded area of the anode rod with teflon tape to ease removing
it next time when I need to unscrew it.

Thanks again for helping me to come up with an action plan to deal
with my 4-years old waterheater.

Jay Chan