If you're lucky enough to have a backyard, then buying an inflatable pool meant for children is a pretty good deal. You can throw your kids in there for a while, or you, an adult, can hang out in a couple inches of cold water alone. It may not be as big or deep as a regular pool, but at least you can have a cold drink while you're "swimming."
There are many methods and vehicles to disperse water, including water guns, water balloons, and sprinklers. Water guns are probably the superior choice, as they are reusable and refillable, while balloons are disposable and also sting on impact. Ultimately, these activities are best reserved for children, because there's something unsettling about the image of a group of adults having a water balloon fight.
This one is admittedly pretty sad. A bathtub full of cold water sounds more like a punishment than a treat. But if it's hot enough that you're sweating indoors, it might just do the trick. Grab a pool toy, like a noodle, some goggles, or one of those floaties that can hold a drink, and you might just feel like something maybe resembling being at the pool. Or you might just feel sad.
Find a roof, lawn chair, or public park (if you're that confident) and sunbathe as if you were at an actual pool. The pros are that you get tan (don’t forget to wear sunscreen!) and get some vitamin D, but the cons are that you might get sunburned and too hot without the relief of cold water at the end. Get one of those spray bottles and periodically spritz yourself like a cat who's misbehaving.
When all else fails, there's always the shower beer. Or shower seltzer. Or, fuck it, a shower glass of wine with ice cubes in it.
At the end of the day, none of these activities can ever replace a tasty dip in the pool, but we're in the middle of a pandemic, so all your summer experiences are going to be replaced with a paltry version, but that's OK. At least you're alive!