Deildartunguhver () is a hot spring in Reykholtsdalur, Iceland. It is characterized by a very high flow rate for a hot spring (180 liters/second) and water emerges at . It is the highest-flow hot spring in Europe.
Some of the water is used for heating; it is piped away to Borgarnes and away to Akranes.
A fern called Struthiopteris fallax, grows in Deildartunguhver. This fern is the only endemic fern in Iceland, and it does not grow anywhere else in the world.