In response to the edited conditions, I am thinking that, assuming you don't want to kill (by addiction withdrawal) people who stay at home for more than a week, or homeless people who may be living in parks or sewers or garages or wherever, this eliminates several options. All humans only need a few things regularly - in order of importance: air, water, food, light, clothing. You say you don't want to use water, and you don't control the food, light seems unlikely to provide a drug, and I assume you don't control clothing if you don't control food (but that's another idea). In that case, I think you want the drug to be everywhere, so in the air, either in dust form or vapor or gas. Since this is a high-tech megalopolis, there are probably air conditioning/heating/"cleaning"/ventilation units all over the place, which can be used, especially if you lie about some wonderful cleaning or scenting agent that the drug can be mixed with.
On the other hand, if you actually like that homeless die off rapidly (I notice you didn't include a homeless class in your four classes), then you could have the drugs distributed at shorter range, or only in orthodox regulated areas, so that people who try to live in sewers or parks or wherever, will be addicted to coming to orthodox places, and need to leave or die of drug withdrawal, unless they somehow manage to stay away enough to not get addicted, or manage to detox by carefully staying on the fringes. This could be accomplished by having airborne drugs that dilute out after a limited range of dispensers which are all in orthodox areas (e.g. by ventilation units or certain paints). If your high-tech city is designed such that all people will need to use a vehicle of some sort every seven days, the drug could be applied in the vehicles.
Since ventilation units are the most obvious way to add something to the air, you might want to do something less predictable. Ubiquitous fire extinguishers, lighting units, fire/gas alarms, wifi network hubs, electrical outlets - any ubiquitous appliances or technology could have gas secretion units added. You could also (or instead) have some nanotechnological agents which produce the drug invisibly. Or use off-gassing from paints or other common building/paving materials. A recent Earth invention is also paving slabs which are solar panels with computers in them with LED that can display changing road markings - if such things were everywhere, or if any computer systems were everywhere (as is already happening on Earth with computers in phones and appliances and cars etc) then some fraction of those could include micro-devices which produce the drug - one detail could be that the supplies for the drug production could be added to the chemical batteries used for many computers, so replacing the batteries means replenishing the drug supply.
Another mechanism which doesn't involve the air could of course be required personal devices, either implants or computerized battery-recharged ID cards, or required cell phones. Or nano-robots which invisibly find and inject people. Or fingerprint ID door locks and light switches etc everywhere which administer a contact drug (but habitual drug users would start to experience withdrawal).