The Drip, Part 1 is a story published in Teenage Mutant Ninja Turtles: Amazing Adventures issue 13.
An overworked and worn-out Donatello is attempting to synthesize a Retro-Mutagen for Splinter, when he dozes off just long enough to cause a chemical reaction which leads to his lab exploding. Donatello walks out and proclaims that he's "okay", before passing out.
Coming to, the other Turtles convince him to take a week's break due to his overexertion. However, Don had eyed a bottle of sports drink ("Refresh-aid") that Michelangelo had been drinking, and takes it away to add a tiny amount to his Retro-Mutagen attempt, hypothesizing that it could be the bonding agent he was looking for. The result is actually to create a small pink liquid mutant, which he calls Drip. Don seals The Drip in a jar and goes to sleep.
In the morning, he sees that The Drip is dehydrated. He goes out to the kitchen to get some water (while Mikey freezes his tongue to a slice of pizza he'd dipped in liquid nitrogen), and gives a bit to The Drip, who perks right up.
That night while everyone was sleeping, The Drip got out and suctioned out all of the water in a mug Michelangelo was drinking out of, then found the leaky faucet of a sink and went after it. Donatello woke up to find himself completely submerged in water.