I'm cooking up a custom that has 2 parts.

Part 1 is a remake of a public kissing challenge video on YouTube that I like except the prankee is wearing a dress.

Part 2 would be them continuing to kiss in the shower, except the girl still has her dress on and is getting soaked.

I know that it's my video and I can suspend reality however much I like, but I still want to retain some logic to it (ie there needs to be a reason she's suddenly in the shower with a dress on), and "how much money would it take for you to come back to my apartment and get in the shower with that dress on?" is all I could think of.

So, the question: what would it take to convince a non-wammer to get wet fully clothed?

One reason might be if the dress is messy, so hopping in the shower is the best way to clean it up. (Similar to the "washing off" segment at the end of some WAM videos.)

Another reason might be "I've always thought that it would be really romantic to kiss in the rain. It's not raining, but we can use the shower to pretend, and the water will be warmer."

Either way, there would be a practical aspect: what will she wear after the shower? I.e. can the dress be dried out, or are there other clothes she can borrow?

I was also thinking "washing off" is a logical answer to why someone would shower fully clothed.

I don't know what this public kissing challenge is. Are these two strangers that are challenged to kiss?

I am imagining them kissing in the public, and a 3rd person is offended by their public display of affection. The 3rd person does something to get her dress a little messy. They go to a nearby hotel room to wash off the dress immediately before it stains. The mess on her dress is scrubbed vigorously which leads to sexual touching and more kissing.

Be up front with them or hire a model.

As I understand it, the OP is planning to hire a model for a custom. The question is "What's a plausible reason for the fictional character to stand under a shower?"

Ahhh ok. I thought it was a real situation they were asking advice for.

Some possible scenarios:

They've seen clothed shower scenes in movies and wonder what it would feel like. e.g. the shower scene in Casino Royale.

They previously went to a water park and got partly or totally drenched by the rides, and realised they quite liked how it felt, and wanted to try getting wet fully dressed in a more controlled environment and sexier outfit.

They'd previously been at a wedding or other social event where people got thrown into the pool, they were too nervous to let it happen and hung back, but seeing a quite adventurous friend coming out of the pool in her soaking wet formal gown and seemingly loving how it looked and felt, has had a hankering ever since to try getting soaked in a dress.

She's bi/pan and poly, and one of her girlfriends is into WAM, and so she's either previously done it with said girlfriend, or watched the g/f getting soaked for pleasure while staying dry herself, and again, is now curious to try it.

She's seen people get soaked fully clothed on TV in gameshows or news reporters going into swimming pools, and it's aroused her curiosity.

A millionaire splosh producer she met in Vegas, when she was there for a friend's wedding which just happened to co-incide with the dates of a UMD meet, put her up to it and offered her a grand for the footage if she filmed herself doing it.

She's already into wetlook as a full on fetish and gets soaked in clothes constantly, but usually sportswear - this is her first time trying it in a dress.