Tin foil cover came off in autoclave. Is that ok?

I work in a freshwater ecology lab and rarely do I need to use my department's autoclave. A student took some stream water samples and had them sent to the lab for me to autoclave. Our media bottles for whatever reason can be autoclaved, but I was nervous about the caps, so I covered with tin foil. I guess I covered too loosely because they came off during the cycle and were in the tray.

Is this ok for the cover to have come off? It's literally just water, it looks like more evaporated out than it should have, just curious if there is any concern for having lost stream water to evaporation?