Chances are the person who owns your park is operating it in hopes to turn a profit. One thing that you find is bills have a tendency to go up. The same thing can often be true for a mobile home park operator.. Property taxes might go up, payroll, their admin expenses , professional dues, professional services etc. These costs then get passed onto the customer just like when fuels costs rise, yo would see this as your end result say when buying a gallon of milk.
Perhaps the water increase was originally thought to be the solution but consumption surpassed and the increase did not cover it.
Again, we don't know all of the specifics but those are some possible items that can give you insight as to why an increase might occur.