Some fungi produce a waxy material during the natural process of breaking down organic matter. This wax can coat soil particles, especially the large soil particles of sandy soils as well as some gravels. This wax coating then prevents water from entering the soil, a condition known as hydrophobia or water repellence.
Most of our sandy soils become water repellent as the weather warms up and the soil dries out. On a sloping site water may simply run off instead of soaking in. On a level site the water will pool and only soak in a few small areas leaving most of the soil dry. This is a very common problem in lawns where it leads to dry patches developing. Many people react to dry patches in their lawn, by applying extra water which, while it may eventually overcome the problem, also wastes a lot of water.
A far better solution is to apply a soil wetting agent which will allow the water to soak in where it falls.
Soil wetting agents are specially formulated surfactants which break down the wax barrier. They must be activated by water to be effective. In practical terms this means they should be watered in thoroughly immediately after application.
Bluegrass Lawnmowing will happily assist you with your Soil Wetting Agents.