Q: MacBook Mac OS X 10.5.8   "t" key does not work. Maybe water damage   How can i fix it?

Replace the keyboard.

The keyboard doesn't reboot. It is only reset when the computer is rebooted. The only way to determine if it's a software issue is to reinstall OS X.

You may be able to see what if any effects the keyboard may be trying to perform by using

the Keyboard Viewer, because you can use the mouse to choose other keys, among other

details from the Viewer. Troubleshooting may include trying to see if just the single key itself

has a defect. Some online sources suggest how to clean any debris that may be under one

key, and others offer specific parts to the kind of keyboard your computer model has in it.

Some companies offer keyboards or key parts, and at times OK-used parts may be offered.

An example of one that has a variety of stuff, (I've not any experience with) is this...

http://www.powerbookmedic.com/

A place that may (or not) have some bits:

http://www.replacementlaptopkeys.com/

For awhile, I'd guess you may have a spare USB keyboard to use until this issue is resolved.

If it happens to be a windows PC keyboard, you could still use it, so long as you know & use

the correct alternative keys to make the Mac actions work. All mine are only Mac keyboards.

And I look for spares when not needed, to use with portable and desktop Macs.

•Keyboard Mappings using a PC Keyboard on a Macintosh: (microsoft support)

https://support.microsoft.com/en-us/kb/970299

Another look at this situation, which also confronts dual-boot OS X + Windows Macs:

•Boot Camp: About keyboards and key assignment for Microsoft Windows - Apple Support

Anyway, hopefully your MacBook can find its 'T-key' again without surgery!