Is there a way to test the salinity of bilge water without putting it in your mouth?

Even though I keep a fairly clean bilge, that stuff can be nasty at times. It only takes a drop of oil for me to want to keep it out of my mouth. I've been battling very minor leaks in my fresh water system and I'm often wondering if the water getting into my bilge is fresh or salt. And yes, I've tightened every hose clamp I can find, but I keep finding new ones in very inaccessible places.