The answer to 'why is my irrigation system thin grass' is that there are several common causes, including improper sprinkler head adjustment, system leaks, and issues with the water pressure or flow. Thin, patchy grass is often a symptom of an irrigation problem that is not delivering the right amount of water evenly across the lawn.
Some common causes include sprinkler heads that are not angled properly or are obstructed, causing uneven water distribution. Leaks in the irrigation pipes or fittings can also lead to dry spots. Additionally, if the water pressure or flow rate is too low, it may not be adequate to properly water the entire lawn.