In my view, unless it is the first season of planting, watering plants in the ground is not required, unless the weather is exceptionally dry (rarity in British climes, so it seems). If you need to water after the first season, it sounds like you got the wrong plant in the wrong soil and/or location, or you've not prepared the soil to retain moisture or encourage root growth, both of which help to eliminate the need to water.
Not watering plants, encourages plant roots to seek out moisture deeper into the soil, and stops plants putting roots near the surface which makes the plant more susceptible to dry conditions. The only thing I now water (using water stored in water butts, not clean expensive tap water), is my pots and even those I do sparingly to prevent too much sappy growth which requires even more water. When I plant, I dig a whole twice the size I need, and throw in old compost and well rotted manure, both of which help retain moisture. I also throw in a large handful of blood, fish and bonemeal to encourage good root growth. Works for me.