Notifications in constant loop (Blynk) trying to trigger along with serial function
Your code:

timer.setInterval(16000L,notifyOnButtonPress);


Is calling this function every 16s.

This code:

if (floatLevelLow &amp;&amp; floatLevelLow != floatSavedState) {


needs some parentheses to force your desired order-of-operations. As it stands now, you are asking the result of floatLevelLow &amp;&amp; floatLevelLow and comparing if that is not equal to floatSavedState. That's likely not what you want.

Did you mean: 

if (floatLevelLow &amp;&amp; (floatLevelLow != floatSavedState)) {


EDIT:

Also, your if/else is missing brackets around the 2nd clause and should be:

} else if (floatLevelLow != floatSavedState) {
     // send notification if this is first time or if the float level has
     // changed since the last notification.
     Serial.println("Resevoir Water is High!");
     Blynk.notify("Alert : Water level high");
     floatSavedState = floatLevelLow;
}