Gavin Rossdale and Gwen Stefani bathe together - to avoid wasting water. 
Gavin - who has sons Kingston, two, and six-month-old Zuma with his wife Gwen - insists sharing a bathtub with Gwen is a good way to help the environment.
He said: "All families should bathe together. It's the least they could do!"
The 43-year-old rocker also advises recycling and fitting solar panels to help save energy.
Meanwhile, Gwen, 39, has revealed she and Gavin have a new nickname for Kingston because he is currently going through a troublesome stage.
She said: "Kingston is in that terrible twos. Gavin calls him Sid Vicious. He's like, 'You gave birth to Sid Vicious.' He's definitely got an attitude and Zuma is the opposite. He's like this cool, laidback, easy-going guy - is that always how it is?"
Kingston has inherited both his parents' love of music, and already has a keen sense of the songs he wants to hear.
Gwen explained: "He likes Top 40 hits like his mom. Any song that comes on, he'll get p***ed if you turn the station. He'll be like, 'That's my song! That's my song!' "
The 'No Doubt' singer also revealed her secret to getting back her pre-pregnancy figure - carrying around Zuma.
She laughed: "I have this little chunky baby. Zuma is like the biggest, chunkiest boy. He's gigantic. He actually gets my arms strong because he weighs so much carrying him around!"