Open-water sessions are an ideal way to prepare for open water races (triathlons and swim marathons). However, there are many swimmers who might not be able to do this for various reasons. Do not fear it that is you. If you have access to a pool, you can still prepare very well and have a successful swim on race day.
Include longer swimming sets in your practices. It is important to swim several times the distance that you will complete during your race. Keep in mind that during you swimming pool swim you have extra rest on the wall. That is why, during practice you could also extend the distance that you will complete during your race. You could also train open-water turns or lifting your head for better sighting during your race (Tarzan drill – swimming with your head up).
Overall, even in the pool you could familiarize yourself with the conditions that you will have during the open-water race. If you add some creativity you could achieve wonders.