Fairy,
In theory, it is possible to contract HSV from indirect contact with objects, such as towels, cutlery etc, or hypothetically I guess via transmission in a swimming pool.
In practice, the risk of transmission of this type, and in particular via the swimming pool is so small as to be effectively non existent, for several reasons;
1. Dilution effect of being in a large body of water
2. HSV can survive only a very short time outside the body - with chlorine about, that survival time is reduced still further
3. You would need a route available for the virus to enter your system, ie a lesion, cut etc on your lips.... the odds are in your favour.
4. If you already have HSV, your immune system will have developed antibodies to it, so even if all the other factors failed to stop it, your immune system should protect you.
Personally, I think you only really have to be careful of exchanging body fluids with someone who is infected, so that means in addition to the obvious, such as kissing etc, not using intimate objects, such as towels, toothbrushes, cups, cutlery etc shortly after someone else has.
Finally, lip balm SPF15. My feeling would be that is too low. The only time my cold sores erupt nowadays is through sun exposure or serious chill factor... so I use SPF 30 or more on my lips when I am outside for any length of time.