Jar, there are 2 basic ways to defeat a drug test. Read the SUBSTITUTION and DILUTION links at the bottom of my post.
If the test you are taking is a instant type of drug test AND there are no urine validity checks, then yes, a few drops of water in the 'hole' will give a passing test result. If the test has a urine validity check for pH, Specific Gravity and or Creatinine, then water will not work.
I'll post links to the type of test that water will work for.

This type will pass. http://www.meditests.com/urdrugofabte1.html

Hope that helps. N2