Bladder

The Bladder meter decreases naturally throughout the day, and can only be increased by going to the toilet. Upgrading to a better toilet can boost Comfort whilst the Sim is relieving him or herself. The bladder meter decreases rapidly with a cup of coffee definately and is harder.

Bladder Meter Completely Decreased

The bladder meter decreases while the sim tries to hold also. If the bladder meter is completely red and they cant use the toilet the sims start to get cranky. Now it is urgent and something that cant be helped is when the meter is continuously red and the sim cant use the bathroom that leads to serious embarrassment where the sim pees on the floor. If that happens that also decreases the hygiene meter.

Toddlers

Sims have to train toddlers in order to let them use the potty by themselves. They will wet themselves if not potty trained. An older sim can click on the potty chair and potty train the toddler.

Public Toilets

As a rule, community lots will have public toilets of some sort. In The Sims 2, Knowledge Sims and/or neat Sims may occasionally have a fear of using a public toilet. Having an accident is a fear on The Sims 2, and it takes away more influence than aspiration.

Outgoing and Sloppy Sims

In The Sims 2, Outgoing and sloppy Sims are also able to "use" shrubs and the AquaGreen Hydroponic Gardento relieve their bladder needs. Sloppy Sims will also pee in the shower if their Bladder need is low enough. In The Sims 2: Pets Werewolves can use the Howl Interaction to Lower Non-Werewolves' Bladder Needs

Sims 3

In The Sims 3, the Steel Bladder Lifetime Reward makes it so that Sim who purchased it no longer has to use the bathroom again. In The Sims 3: World Adventures , Mummies do not have the Bladder Motive at all. Also the sim gains a moodlet for wetting themselves called "Embarrased" which gives -20 mood and makes hygiene 0%.

Trivia

 * The Sims Medieval features no Bladder meter. Instead, a Sim using a chamberpot gains a temporary buff.