It's my understanding that lorazepam (Ativan) intended for injection comes as a solution in propylene glycol. I suspect it is one of the more water-soluble benzodiazepines but as a class, benzodiazepines are not very water soluble.
It's used in ICUs since it has no active metabolites so a patient's liver and kidney function will not alter the pharmokinetics of the drug.
In the old days psychiatric units in the UK used a mixture nicknamed 'B-52' which was 5mg haloperidol, 2mg of lorazepam. I find that a very scary idea.