Theoretically, one can perform one wuḍūʾ for Salah and this wudu would be considered valid for the rest of the day, unless you nullify it by certain means. Muslims believe that certain acts invalidate the wudu (often referred to as 'breaking wudu' and 'losing wudu'), although the Qur'an does not explain most of these, and rules differ among schools.
According to Sunni Muslims
According to Sunni Islam, the following invalidates wudu:
Slow-wave sleep while reclining.
Sleeping with the help of support.
Loss of senses.
Fainting.
Defecation or urination.
Odorous or audible emissions of flatulence.
Ejaculation of semen.[d]
Vomiting.
Touching the private parts with the bare hands.
Blood or pus leaving the body so that it leaves the point of exit.