If you’re willing to go down this rabbit hole: I have a Planck keyboard. It’s super tiny, only weighs 300g and feels good enough that I use it daily for work (programming) even though I bought it for travel. Don’t get too discouraged by the missing keys. It does have a slight learning curve and in my case I also tweaked the software quite a lot to get exactly what I want, but if you’re up for it, it can be super rewarding. I got the pre-built Planck EZ but it’s discontinued but there are other Planck-style boards out there.
I went the easy route and got a Planck EZ because of the plastic case design where the upper part of the case is the plate. It’s super lightweight which was my no. 1 priority. I got mine used but if you plan to buy new, it’ll be discontinued soon, just a heads-up. I’ve seen some Planck-style kits on Aliexpress, some with aluminium, some with plastic cases, but haven’t tried them myself.
I use a Planck keyboard which weighs just under 300g with Kailh box switches and XDA keycaps. It’s labeled as a 40% keyboard so I was reluctant at first, coming from 65% myself. But since the keys are smaller, especially the space bar, it still has a relatively high number of total keys given the small form factor (there’s even space for arrow keys!) and having your layer switch keys right next to the space bar for your thumbs is very comfy IMO. I ended up liking it so much that I use it daily and now I’m wondering what to do with my main keeb. If you’re up to trying something new, you can have a look at some layouts. The keyboard looks inconveniently small but once you see the layer layouts, you’ll see it makes a lot of sense actually!
My first keyboard with standard Cherry MX browns last me a decade despite living with a hairy cat. Whenever I removed the caps, there was quite a bit of dust and hair, but it never got bad enough to affect performance and I cleaned it like once every 2 years? In the end, the reason I swapped it out was because the springs were worn out, not dust. Don’t know about water though.
I bought it from Ebay Kleinanzeigen to be precise, which I think is more like facebook marketplace? There, people prefer to pick up their items in person if possible and you usually talk to the seller beforehand. I’ve had good experiences buying both my keyboards like this. The community is rather wholesome and since there are a lot of people out there who are switching boards like clothes, the second-hand market is quite active, too.
I had a search notification set up on Ebay and snagged a used one for 120€ including switches and keycaps (though I changed those). Since it was in my country, I didn’t have to pay any additional import tax either, just some shipping. Previous owner said that the 40% was too small for them after all so they had to give it away. Maybe have a look out for those ;)
I was also looking for a small and lightweight mechanical travel keyboard and just decided to go with the prebuilt Planck EZ from ZSA. The reason being the case. I wanted a case for some protection because it’s a travel board but it had to be light. The EZ’s case has a top side that doubles as the plate, so it doesn’t add that much weight. My EZ weighs 297g including switches and keycaps and you can barely go smaller than that.
Does ash count?