Here's an interesting little demonstration of poor watering: the other day, a client asked me if I would keep their nephew occupied for half an hour, so I gave him the hosepipe and asked him to water a herbaceous border.
Ten minutes later he was done, so I set him off dead heading the Buddleia (a never-ending task) and went to the border and dug a small hole, vertically down into the ground, to see how deep the watering had gone.
In the picture above, you can (hopefully) see that I dug down to the length of my finger, then scraped it out sideways so I could take photos - it's not that easy to get a picture of it, but can you see that there is a darker slice at the top of the soil? That's the bit that was soaked.
With my finger for scale, you can see that the dark layer is barely 1” deep - and all the rest of the soil is bone dry.
From this, we can clearly see that ten minute with a hose, on dry soil, is not enough. He was fooled by seeing water puddling on the surface, and running off sideways, into thinking that he had watered sufficiently, whereas really he had watered too fast.
When I water with a hosepipe, I start at one end of the bed, and work my way slowly along it, swinging the hose from left to right so that the water around each plant gets a chance to soak down, rather than running away across the surface: by to-ing and fro-ing, each plant gets several short showers, rather than one longer one, much of which is often wasted. I also shake the hose up and down as I am swinging it from left to right, to mimic gentle rainfall, rather than sand-blasting the soil away from the roots of the poor plants. All this is to give the water time to soak in, so that more of it goes down into the soil, and less of it runs off into the lawn.
Next time you are watering with a hose, take the time to dig a small hole afterwards, and check how deep your watering is going: most plants have roots 3-6” deep, so if you are only wetting the top inch, as happened here, then your plants are not going to get much of a benefit!