One thing that my kids LOVE to do outside is squirt water. So we bought some cheapy little party favor squirt guns to entertain them but they had to be refilled every couple minutes and ultimately broke within a day or two. I started saving my dish soap bottles and, after a few good rinses with cold water, they’re a great substitute for squirt guns. Sometimes we put food coloring in the water and they call them their rainbow squirters. These are also a lot of fun in the bathtub!
Let them water your plants!
Another way we play with water is to have the kids water plants. Our daughter, Miss S, loves to water every bush and rock she sees until she’s soaking wet and covered in mud. It’ll entertain her for a good hour or so at least. So we gave Miss S a cleaned out gallon milk jug as a watering can. My husband used a tiny bit to drill holes in the cap to let the water out. We’ve also done this with 12 oz. water bottles and plastic juice containers.