I'm only 20 shaves in, but have already seen water spots. Being very methodical about drying the blade with tissue when I'm done, I never had a problem rinsing throughout the shave. I noticed first slight spotting the day after I'd left the razor on the counter just a bit too long mid-shave. Luckily, a little blue magic polish took the spots off very easily.

About the water usage. As a DE shaver, I really like Mantic's videos but - I hate how he leaves the faucet running heavily in many of them. I just turn on the faucet a moment to clear the bulk of cream and hair off the blade - with the tang up so I don't get water in the scales.

Good question. I was surprised at how little it took to start the oxidation, even when I thought I was methodically cleaning after each shave.