Hi Giorgio,
I live in Belgium, in a region known as Campine in Italian. We have a sandy and infertile soil that does not retain water well. So even though we have about 800-900mm precipitation annually, we always have issues during hot spells and drought due to poor soil (almost every year).
I “solved” this problem by making raised beds filled with (mushroom) compost (20-30cm). The difference is immense. As a matter of fact, I never thought of watering the plants during the drought, but rather of saturating the compost with water. Once a week was fine, though I was quite liberal with water. My crops grown outside: beetroot, cabbages, beans, celeriac, carrots, parsnip, leek, tomatillo, zucchini, squash. I watered onions once a month. Things have been and are growing great.
I have other parts were I only topped the soil with a few cm of the same compost, but plants didn’t do very well. Many died… 🙁 While topping the soil with compost certainly helped boosting fertility, it didn’t result in a miracle under the extreme conditions of the last two months, but the raised beds did!