Swansea climbed five places to 13th after beating West Ham 4-1 last weekend - their biggest win of the season - and moved above Huddersfield on goal difference.
"When I arrived people said that to stay in the Premier League - like I expect - will be some kind of miracle," Carvalhal said.
"But this is not something that is divine, it is part of this world and about hard work.
"We are fighting and we have used a lot of water to put things in a good way.
"But it is like a forest where the fire can start again if you do not check for it."