Tri-Suit or Wetsuit
Hi Mark = check out the website for each race the rules will stipulate wether you are required to wear a wetsuit or not. Most open water swim will insist you do. I know London does. I will be wearing one for all my open swims with a tri-suit on underneath as I imagine most will. Have a look at other posts on here and you will see many advantages to the less experienced wearing a wetsuit for the swim.