How quickly does the BPA leach from a plastic bottle to the water - when should I toss the unused portions of a case of water?

I bought a case of water and used about half of it – the remainder has been in the back of my truck, unprotected and getting full sunlight day after day. (2–3 weeks)

How quickly does the leaching take place? Is it quickly, or is it an ongoing thing? Should I just throw out (or recycle) the rest of the case?