Reduced precipitation can lead to limited water availability by reducing the amount of rain that we get therefore there is less water. Without the rain the earth would eventually dry out and there would be no more water to use.
Let's think in Brazil as an example to answer this question, and the Amazon forest.
Explanation:
The amazon forest is one of the biggest forests of the whole world, being responsible for a lot of the water distribution there is in Brazil due to a process called flying river. The water vapor that the trees in amazon produce is very high, we can check on that by seeing how the weather in this region works, it rains almost all the time, and then, this vapor water spreads across all the country and other countries too. If there's a problem in amazon such as fires and deforestation, the amount of water that is going to other regions of the country is less than before, and in that way, the water availability will not be enough anymore.
