After motor has cooled and sat for a few hours ... check the condition of oil on the dipstick. If it's "milky" appearing (kinda looks like a chocolate shake) ... it's usually caused by water in oil (bad).
Did you pour water onto the head while valve cover was off (bad)? If so, the water may've run down the pushrod holes and into the lower engine (bad). If all this is true ... change the oil & filter now ... do not wait. That done, the residual water will cook off in short order.
On the other hand ... If the steam ceases by the time the motor's up to full operating temp ... then it's probably OK ... probably just daily/nightly condensation forming inside exhaust system (Most any car will do this when humidity & temps are right). But ... If it persists after motor's hot ... then you have problem (blown head gasket/cracked head etc). Let's hope it's just routine condensation.
JACK:gap