Tomatoes, which have been preserved from the summer months, are also added to the mix with a bit of salt and olive oil.
"It's a nice and nourishing way to sustain the school community," parent Rebecca Thompson told Kapiti News as she helped set up on a bitterly cold Thursday lunchtime.
"And the kids love it.
"Only on one occasion did we have enough left for seconds."
She said 15 to 18 litres of soup was made each week on average although it was about 30 litres when the editor was there.
Parents have a couple of recipes they can follow, one featuring roasted vegetables and the other where everything was grated.
Pupils, who are encouraged to bring their own cups and to rinse and wash the cups afterwards, also get a slice of toast which has been supplied free via a supermarket.
Parent Shona Jaunas, who was distributing cups of soup, said the soup was gluten and dairy free too.
"That's just to make sure it's available to everyone."
Pupil Taliyah Farrell, 11, said the soup was "good and burst with flavour".