  Is this pepper safe to eat? Most of it looks fine , just very watery texture.  
It's no less safe than any other pepper, unless it's worse than it looks in the photo. Check carefully for signs of mould. The texture will have suffered, so it's probably not great raw,  but I'd cut out the brown bits and cook the rest, and often do, as I buy big cheap bags of peppers and the last couple can hang around for a while.  Most people who grow their own veg would trim and use it without question 