Only my opinion, but a week is a pretty long time to allow a boa to soak. Dirty water is a great place for bacteria to grow. And even if it looks clean, its guaranteed that if a snake has been sitting in it for a week, its not clean. Around the edges of the mouth and in the mouth is where a snake will develop stomatis, commonly known as mouth rot. It's bacteria growing in the soft tissues of the mouth. Sometimes a snake will feel it and try to rub it off, but it wont. If stomatis is setting in, it will require a trip to the vet and some antibiotics to remedy. It is not difficult to remedy it caught early, but if left untreated, it can become serious, even fatal.
My recommendation is to use water bowls too small for your snake to get into, and if you want to let her soak for shedding purposes, put a larger one in for a day, then take it back out.
Just my $.02
Best of luck,
Mark
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uncommonboa.com