yellow leaves = too much water?

I have my first hydrangea this year, a lacecap called Princess Lace. It has done beautifully in the place I've planted it, and even has three flowers on it that I'm excited to see open! Most of the leaves are healthy and green, but I've noticed recently a few yellow leaves - mostly on the inside of the plant, but a few on the outer branches too. The yellow leaves either fall off or come off easily when I touch them. It gets watered when it's hot via sprinkler when I'm watering the grass.

Are the yellow leaves an indication of too much water or something else?

Thanks for any advice!

And here's a photo of the whole plant ...

It could be too much water, or too little water, or stress created by uneven/inconsistent watering (first too dry, then too wet). I'd check the soil regularly by sticking your finger down a couple inches--if it still feels pretty wet then hold off on watering, but if it feels really dry then you probably need to be watering more.