Swimming pool

The Sims
Swimming pools can be made in Build Mode. You can buy a diving board, and, if Vacation is installed, a pool slide. Swimming builds Body skill, and Sims think it's fun. Sims can drown if they use up their energy, so make sure you have a pool ladder in the pool.

The Sims 2
In Build Mode, a pool can be built on lots. A pool is useful for keeping your Sim fit and increases your Sim's Body skill. If you buy a diving board, your Sim can Dive. They will get better and better at diving. A Sim can drown if there is no means of getting out of the pool, so be careful.

With FreeTime, swimming increases Enthusiasm in Fitness.

Prior to Nightlife, building a pool in The Sims 2 was extremely cumbersome. Extensions to the pool needed to be a minimum of 2 squares and all pools must've been rectangular or square. Nightlife introduced the diagonal pool tool and fixed the problem regarding pool construction.

If Seasons is installed, you can also use curved pieces and a pool slide.