I had this idea as I was drinking water in my bed and daydreaming about Demerald.

The car ride to visit Gilbert's parents was long and tiring. Especially since it was such a warm day. Gil was stuck in the back seat with his boyfriend, Mattie while his brother and Feliciano. His husband, were up front.
"Uh guys...ve have a problem." Gil announced about two hours into the trip. "Ve're out of vater." Nothing was left in the cooler they had packed in the back seat and they were far from a grocery store at the moment.
"Schieße." Ludwig swore.
Feliciano pouted. "How am I gonna make pasta now?"
"How jou make pasta in a car in zhe first place is beyond me." Ludwig rolled his eyes.
Gil looked to Mattie, who hadn't said a word.
"Mattie?"
"I have a little water left from my last bottle..." He admitted.
"Can I have it?" Gil asked, putting on the cutest face he could muster.
"Well...I may have back washed a bit..."
"Matthew, isht not like I haven't had had worse in mein mouzh."
"Ew." Matt grimaced and blushed.
"Kesesese~ Can I have zhe vater now?"
"Fine. Just lemme take a sip first, okay."
"Okay."
Matthew took his water bottle out of the little hole in the door and unscrewed the cap. There was about a large mouthful left and Mattie managed to take in the entire thing.
"Maaaaaaaaattttttieeeeee!!" Gil whined. Sure, the way his boyfriend's cheeks were all puffed out like a chipmunk's was cute, but still not worth dehydration.
Mattie grinned as much as he could without letting the water out.
"Are you just holding it in your mouth to tease me?"
He nodded. The little shit.
Two can play at that game, though.
Gilbert leaned forward, kissing Mattie with the intention of drinking the water from his mouth.
The end product was now warm and kinda gross but it was still water. A bit did get on their shirts, though.
"Thank you for the meal, Mattie." Gilbert bowed, but Matthew didn't hear him, he was laughing too hard.
"I love you, Gil." He choked out, taking the Prussian's hand with as much sincerity as he had left.
"Ich liebe dich auch." He said back.