I always say to them when they first arrive to let me know if there's anything I can get them beverage wise like a cold drink or a cuppa, that way I've put it out there that its okay to ask for it, but its on them to ask. Of course, up here tradies get hot and bothered pretty quickly so if I think they really need a drink and are just afraid to ask or something, I'll just put a glass of ice water out for them as if they're Santa or something