In Meridian, there is a pool owned and operated by the Western Ada Recreation District. It is located off Meridian and Franklin Rds behind Storey Park. I have been swimming there with my kids and it is a great pool. It is reasonably priced and they have recently added a splash pad and shade umbrellas. There's a high dive and a low dive, but no slide that I can remember. See their website for entrance fees, operating hours, and information on swim lessons, private parties, open swim hours, lap hours, and free swim day.
Boise has many city pools. Borah Pool, Fairmont Pool, Ivywild Pool, Lowell Pool, South Pool, and The Natatorium Pool and Hydrotube. My sister was on a swim team and we got to spend a lot of time at these pools. This summer I plan on taking the kids to the Hydrotube. I've heard great things about it and I think they would love it. Click on the pools above to find their location and more information about what each pool offers. The City of Boise also has this fantastic website that tells you all about swim lessons, swim team, parent and child swim time, pool events, pool parties, and it has a map that shows you where all of the pools are located. If you are new to town you might want to check out the map to see which pool is closest to you.
Also, if you think you'll be doing a lot of swimming at city pools this summer, I recommend buying a season pass which is good for all the outdoor city pools. There is a resident price and non-resident price. See the list of admission prices here for all the Boise city pools. (The Hydrotube is not included in the season pass).
Nampa has a fun waterpark you might want to try. My sister-in-law has taken her kids here for years and she loves it. It's Lakeview Waterpark located near Lakeview Park off Garrity Blvd. I've been to Lakeview Park a few times but never knew that there was a fantastic waterpark right there. It has a zero-entry beach (great for small kids who want to enter the water), a gigantic water slide, spraying water toys, and a nice pool house with restrooms and showers. And it's very affordable. Only $1.00 for kids under five, and $2.00 for kids 6-17, and adults 18 and up are $3.00. We'll have to check that out this summer too.
Nampa also has a city pool called Lincoln Pool in Lions Park along Davis Ave. It has a diving board, a splash pad, a toddler area and a slide. They also have great indoor pools at the Nampa Rec Center.
Caldwell has Caldwell Municipal Pool at 512 Harrison. It has two slides and two diving boards and goes from 2 ft deep to 12 ft deep.
The YMCA also has three indoor pools in the area. One in downtown Boise, one in West Boise off Cloverdale and Chinden, and one in Caldwell off of Indiana Ave. We've been to all three Y pools and the one in Caldwell is our favorite. (Although I am still really upset at the lifeguards for making me take waterwings OFF my two-year-old. They say they are not safe. I say let me be the judge of that and if you see her drowning with her waterwings on, go ahead and jump in the water and save her.)
If city pools aren't your thing, you can always try and befriend someone with a backyard pool or a neighborhood pool. Or if you are more of an introvert like me and you don't have any friends, then I suggest doing what we did and buy an Intex pool for $149.00. We have one that is 12 feet in diameter and 39 inches deep and the kids and I swim, or in my case sit, in it almost everyday in the summer. Even my husband jumps in with us after he gets home from work. We absolutely love it!