It’s probably a leaking heater hose or connection of some sort associated with the heater. Take it to your Holden dealer who I imagine would be able to fix it under warranty.

The Holden Spark has been discontinued in Australia, with the company citing low volume as the main issue. But if that doesn't deter you, it's still a solid buy at under $15,000. Dealers have plenty of stock still on showroom floors, and you can get really good prices on 2017-plate models for less than $15k, drive-away. Shop for the LT if this is the car you like most, because it has a better features list than the LS.

Probably best to steer clear of the regular Barina, which is admittedly bigger, but definitely not better. The current-generation model could find its way to the automotive graveyard this year, too. 

The Mirage isn't as good as either the Barina or Spark, so unless you just want a very inexpensive car, it's not high on our recommendation list. The Yaris is lagging behind the times in terms of features, but there's a reason it's a go-to for many budget car buyers: it's a strong offering for space and comfort. 

All of that said, the Kia Picanto is the budget car we'd most likely recommend, because it has a strong and long warranty and is the only one in the mix with auto emergency braking (AEB). Plus it has a reversing camera as standard (the base model Spark doesn't).