These are what we call the 'YMMV items.' Things that some people find in this work. We call them 'your mileage might vary' because not everyone sees these things in the same way. This starts discussions in the trope lists, a thing we don't want. Please use the discussion page if you'd like to discuss any of these items.
YMMV: H2O: Just Add Water
Base Breaker: Emma. She's either a well-meaning girl with a few neurotic tendencies or a bossy and controlling harpy who tries to lecture her friends every chance she gets.
Fridge Logic: So how do they avoid being seen in the school loo? Do they just not go in public?
I'm not sure why that would be problematic for them. People don't normally get splashed with liquid when going to the bathroom, if they're doing it right.
Yeah, but do they just use Purell or what?
Brought up in-series when Kim notices she's never seen Cleo washing her hands.
They have ten seconds to dry off before the change kicks in. That's enough time if you're quick, have paper towels handy, and maybe wash them twice.
"The Siren Effect" - Cleo says it's a Wednesday. So why is she having a sleepover on a school night? And why aren't the girls getting ready for school the next day?
Germans Love David Hasselhoff: It's a hit in The UK, Central and Eastern Europe, to the point that the 3rd season aired in the UK first before Australia got it... by a year.
Doing rather comfortably in the U.S., too.
Moral Event Horizon: Charlotte crossed it when she in the second-to-last episode stole Cleo's lockett and made her believe that Lewis no longer cared about her.
The Scrappy: Good God, Kim. Many, many of the show's fans have expressed the deepest desire to punt her through a window for her constant attitude.
Take That, Scrappy!: She does get plenty of slapsticky comeuppance though. She gets publicly embarrassed when she tries to out the girls' secret, catches the measles, gets sprayed with a garden sprinkler and is dumped by Eliot for being too bossy.
Toy Ship: One episode had Emma's younger brother Elliot trying to ask Cleo's younger sister Kim out. Kim just took advantage of him and kept bossing him around. He eventually got tired of her attitude and ditched her at the end of the episode.