Put the beets in a big pot, pour in water to cover, and simmer for an hour from the moment water has boiled. When done, drain off the water and allow the beets to cool a bit. Peel and grate them coarsely.
Dice peppers and onions.
Mix water, olive oil, vinegar, sugar and salt in a large pot, add peppers and onions, bring to a boil and let simmer for 15 minutes. Add beetroots and boil another 10 minutes. Then remove from heat.
Put the hot beetroots into clean, dry jars. Screw the lids on tightly and immediately set them upside down. Cool completely.