Completey depends on where you live and where the methadone came from (clinic, pharmacy, different clinics also use different concentrations). I don't even know what country you are from. Where I live bottles of methadone do not come sealed in any way and there is no way to tell whether someone has added water to it. Is there a label on the bottle? If so, what does it say?
A common strength for methadone is 1mg per ml, so in that case 110ml would = 110mg (provided no one has messed with it). In this concentration, the bottle will usually either say 1mg/ml somewhere on it, but in some places it might not say anything about the concentration. There are also some clinics that put each dose in 100ml of liquid, no matter the amount, so someone who is getting 10mg of methadone will have the same amount of liquid as someone who is getting 100mg of methadone. But I think that clinics that do that normally use 100ml of liquid, so the fact that your's came in 110ml makes me think it is probably not the case. Although, does the bottle say it's supposed to contain 110ml on it or are you just going by the measurement lines on the bottle? Then another concentration methadone sometimes comes in is 10mg per ml, but in my experience that is less common (and it should say on the label).
Buying liquid methadone illicitly is inherently unreliable because it is so difficult to know how much methadone is actually in the bottle and many people will add water to the methadone, since the buyer won't be able to tell from looking at it.