Keeping your pigs cool and entertained in the summer can be a full-time job. Some days we are outside dumping and filling pools every few hours to make sure the water is clean and cool. A hot pool of water can do more harm than good to a pig.
I've found these Cool-a-Roo sun shades from Costco to be affordable and a life saver. We hang them low so the pools stay in the shade. We even put our barrel waterers under the shades so our pigs have cool water to drink. It's amazing how these shades can keep the water cool in our 100+ Texas heat. This has reduced the amount of times we have to fill the pools.
We recently tried out one of these sprinkle pools for the pigs and they loved it! It leaks a little where the hoses attaches. I would recommend putting it away when not in use. I left mine out and my pigs tore it. The price just dropped so I just ordered another one. The piglets and adult pigs all enjoyed playing in the pool and trying to "eat" the water coming out of the sides. It was a lot of fun.
Each of the pig pens have their own kiddy pool. We use 2 pools doubled up to help support the sides and make then last longer. In addition to that we built wooden frames to hold the pools for the adult pigs because they will smash the sides down and that causes holes to happen. We stock up on the pools when they are for sale at our local Wal-Mart. In the first picture you can see the wooden frame we built holding the plastic pool. We like to use smaller kiddy pools because they are easy to dump out and clean. The pigs will use the bathroom in the water and they bring in all the dirt so the water gets fifthly quickly.
Past summers we have had misters for both my chickens and pigs. However, the spray nozzles tend to get clogged and it seemed like they were more work to maintain than they did to help. The pigs did not really hang out in the mist or anything.
Freezing fruits and veggies inside of ice blocks is another great way to keep the pigs cool and entertained. We also like to cut up cucumbers and put them in a nice clean pool for the piggies to "bob" for cucumbers. You can also throw in some plain Cheerios or other treats.