The three tris I've done this summer have all been open water. I'm thinking about doing one more sprint (why not?) In October, and the swim is in a pool. On the FAQs for the event they discuss OWS not pools. I emailed them asking if it's serpentine through the pool or dedicated lane and I'm waiting to hear back.
Thought of a couple more things - do they allow a diving start? And flip turns or only open turns? I read an article about how pool swimming can cut your time depending on the size of the pool because you're "resting" on the turns and never really getting up into LT, and how pushing off the wall on turns makes your time faster, thus a short pool requiring more turns would be faster than an olympic sized pool, and certainly faster than OWS where you pretty much don't rest. My curiosity has me interested in how all this effects my swim time.