Water the soil, not the plant: 

As tempting as it may be to spray cannabis leaves to freshen them up or cool them down. It should be avoided. Wet foliage fosters an environment that encourages fungal diseases like powdery mildew. Water the plants' base near the soil surface to ensure it reaches the root zone efficiently.

Adjust: 

A cannabis plant's needs will change throughout its cycle, and you should adapt accordingly. During the vegetative stage, they generally need more water. However, as plants flower, they need slightly less. Some growers find it easier to use a water schedule from the outset. 

Monitor pH: 

If you're feeding your cannabis plants with nutrient solutions, ensure your water's pH and nutrient levels are within the appropriate range for cannabis, typically between 5.5 and 6.5. pH testers are handy bits of kit you can easily pick up online and help you get the most from growing cannabis. 

Conclusion: 

So it's not the hardest thing to get right, but get it wrong, and you will know about it. Prepare and take your time. Form good habits and invest in one of two things that will help make it easier to water cannabis plants.