1 - Scrape the carrots with a knife and rinse them.
2 - Cut them into chunks.
3 - Rinse the celery, leaves included and cut the stalks into chunks.
4 - Peel the onion and cut it into chunks.
5 - Combine all vegetables in a pot with 8 glasses of water, add a handful of coarse sea salt and cover. Let it boil about 30/45 minutes.