solid wood foundation

[Mcceag]

Wasnt there a way to replace the starting foundation with the solid without axing the pre-existing foundation?

also anyone having a problem where water sources eat bottles/ cups?

[Quinafoi]

First question, yes.
At the bottom of the build menu there is a replace material option where you can have your hammer replace existing building parts with others of different quality. Thatch quality only applies to a subset of parts, but all parts have a normal and solid quality variant.

Second question, yes, however only as the client in a game.
If you are spam clicking too fast such as refilling an advanced purifier, the cup may disappear from a client. This is likely an item duplication safety feature. I've only ever seen it happen as a client, never for the host. Basically a filled cup is a different item than an unfilled cup. And the game can't handle it swapping items too quickly for the client, eventually the host may just reject the request and the item is simply destroyed. The only way to avoid this is to do these actions slower if you're not the host.