Frequent watering only becomes advantageous for the weed roots and they would love it more than anything. Apply water slowly and steadily ensuring that it reaches deep down to the roots helping in extensive root growth and does not run off. If the ground is too dry, sprinkle a little water and wait till it is fully absorbed. Water again on the moist ground. You will be amazed to see that if you water a stone hard ground, the water runs off fast and only a little is absorbed.
Moistened soil has a better absorption capacity than a bone dry soil.
Physics says that water molecules has a strong cohesive property and they tend to stay together than fall apart. Roots A knowledge about the root structure and depth of it's branches helps determine when, how much and where to water. The deep water are available to the latter plants while that water on the surface dries up soon. Once water works its way below a plant's rooting zone the water is not available to the plant any longer. In a similar fashion as we intake food and nutrients, plants feed on nutrients too for their proper growth, development and maintenance.