Also be careful with the water if it's city water it can have fluoride or chlorine or both in it. Both are bad for the DVD surface and can harm it. I did this unknowingly to a DVD while back and it played for a while after that, but when you flipped it back and forth in the like your could see where part of the surface wasn’t as shiny, this can also be from the minerals that are in the water, but taking my DVD in, I was told the chlorine and fluoride ate the surface after I admitted to what I had done to my DVD. Also if this happens most places won't replace the DVD for free, because it was your doing that broke it. Make sure you use distilled water.
A cleaning kit though would be best, you can usually get them for under $10 and generally $5 if you all you want to do is clean. Also make sure you clean your DVD player laser lens, if it starts to happen to other DVDs. And if the cleaning doesn't work, just resurface the DVD. Super easy and fast, and gives you one heck of an arm workout if you get the cheap by hand one. I use one when a DVD gets stretches across it's sectors and have never had to toss a DVD out or send it back for a replacement.
Kit