No reason not to as long as it's just water. You would probably want to agitate well when going back into the developer to make sure any water carry-over is mixed in well with the developer. Using a very active developer might be a problem, but at the point you'd be doing this the neg is probably pretty close to done, so I'd think any potential even-ness problems would be minimal.
Finally, you may not want to re-use the developer, since you're slowly diluting it, albeit minimally. OTH, since you develop by inspection, it probably doesn't matter.