Contact lenses are an often annoying, but necessary part of life for many of us. I personally can't function in society without sporting my either glasses or contact lenses. But the float tank is a different situation. You absolutely do not need to wear contact lenses while inside a float tank. In fact, I highly suggest that you do not wear contacts while floating.
Reasons To Avoid Contacts In A Tank
The first reason why contact lenses are unnecessary while floating is the most obvious one. The inside of a float tank is pitch black - why would you need to see? What I personally do is carry a "float bag" when visiting my favorite spa. Inside, I always carry headphones, a change of clothes, sandals, and my contact lens kit. My kit varies depending on whether I'm wearing daily or monthly contacts. If I'm wearing dailies, I just throw a new pair into my float bag. When I arrive for my float, I remove the contacts that I'm wearing and throw them away. After my float, I put on my new, fresh pair. If I'm wearing monthly contacts, I'll include a contact case as well as a bottle of contact solution. Before my float, I'll remove my contacts and throw them in the case. After my 60 minute float, I put them back on. Good as new.
The second reason to avoid wearing contacts while floating is because the salty tank water and contact lenses do not go well together. It hurts enough when you get tank water in your eyes without contacts, but wearing lenses and getting salt water in your eyes in an even worse experience. It feels like your contact lens is simultaneously stabbing and burning your eyeball. I highly advise against the experience.
Our Final Warning
If you do decide to ignore these warnings and wear contact lenses while floating, you should exercise caution and avoid splashing or moving about too much. Avoid touching your face or rubbing your eyes. Also avoid wiping your brow or scratching your face. Any of these innocent, small movements can and will introduce the salty float tank water onto your face and into your eyes.