Obviously, sites vary. But even those on the better drained sites still have a lot of water in the ground. Several novices have said recently to us "But the soil is bone dry!". Oh dear, the old-timers think, they have no idea what 'bone dry' is really like. On clay soils, the water is only an inch or so down, and rain is forecast for the end of the week again!
Watering too much doesn't help your plants. They will be stronger and healthier if they are obliged to put down roots into the moisture below them. Watering will only encourage weak growth and may lead to serious problems if the soil becomes over-wet. This is especially true on clay soils. So put that watering can away!!!
When do you need to water? Obviously anything in a container will need artificial watering. But even plants in greenhouses, if they are planted into the soil, will have access to the residual moisture from the winter rain. Newly planted stuff - cabbage plants for example - will need "puddling in" with a generous watering when planted, but do not assume they will need regular watering afterwards. Check the soil below the surface for water before adding more.
A 'dust mulch' created by hoeing the surface soil to a loose consistency will help retain that natural moisture. So will a mulch of grass clippings, or anything else which slows down evaporation.