How many hours should I wait to drink after taking. 5mg of lorazepam?

Don't drink! I assume you mean drinking alcohol. There really isn't any safe amount of alcohol that you can drink while taking benzodiazepines like lorazepam. Sorry to be so strict about it. If you are finishing your prescription or only taking Lorazepam as needed for anxiety then 12-24 hours after your last dose, & if you are not still experiencing effects from the lorazepam, you can drink alcohol carfully.
Alcohol? Water? Immediately. Alcohol, probably at least 6 hours unless your still feeling its effects.