Is it ok to just leave the water lock on for the series 5?

There is no danger for water hitting your watch in day to day stuff.

Rain, washing hands, sweat etc are all normal functions.

Water lock would impede you from normal operations of the watch.

Your screen will be locked and not active on touch, making it very hard to use if for calls, dictation etc

I would just leave it unlocked unless I'm showering, doing dishes or swimming and just use it!

https://support.apple.com/en-ca/HT205000

Like Chris said, I don’t know why’d you want to, but it won’t hurt anything. It'll just be a nuisance when you try to use the Watch.

Part of the reason for unlocking the water lock is that the sound it makes is to eject any water that gets in the speaker hole. You most likely do not want to let water sit there, especially if it salt water or has a high mineral content, as that will accumulate in the speaker hole if you do not eject it.

If you want to activate the water lock manually from the control panel that is fine.

Water lock does not add any additional water resistant. It just stops accidental screen activations caused buy your arm moving through the water.

Why would you want to? I'm not sure that it is a good idea. See this page from the Apple Watch User Guide. Go for a swim with Apple Watch - Apple Support