Can HOA split water and trash costs by ownership % instead of usage?

This question was submitted by Janis of Massachusetts.

Our 7-unit converted condo building doesn't have separate meters for electricity, water or sewer, and the city bills the entire association for trash. Instead of basing the split on usage, our building lumps them all together as the 'condo fee' by percent of ownership. As single condo owner I pay 15.5% of these fees regardless of how much I use these utilities. Is this legal? I feel like I am paying for other condos use of utilities and trash.