Very few melon farmers around here (zone 7) use any irrigation. In fact, if they plant in anything but sand, they cover the rows with plastic to prevent too much water. If it's a garden, you can water them when they begin to wilt, but not too much. As to taste, if they don't ripen on the vine, they won't have much flavor. Watermelons are ripe when the tendril closest to the melon dries up. Even in an area with a lot of light, or a long growing season, melons don't do well till night temps get to about 75. Sorta like peppers that way. Another use for a melon field: Hunt doves. Guess they like the seeds.