Question 1011052
Rate for the filling is wanted as quantity of water per 1 minute.
Quantity is not known other than as a count of "water bottle".  Therefore, the unit of "bottle" is our only possible water quantity unit.


What is flow rate?
{{{(howMuchWater)/(howMuchTime)}}}.
This is a rate, wording smashed together, but should explain what the flow rate means.


Your example problem gives some data about the rate at which William fills his bottle.
How much water?  {{{1/3}}} bottles.
How much time?  {{{5/9} minute.
What is the filling rate?   {{{((1/3)/(5/9))(bottles/minutes)}}}.


This needs to be simplified, and if possible  (yes, should be possible) form into how many bottles in ONE minute, meaning you will want a final answer showing a 1 in the denominator.


For 7th grade purposes, dividing by a fraction means the same as multiplying by its reciprocal.


{{{((1/3)/(5/9))(bottles/minutes)}}}


{{{(1/3)(9/5)}}}


{{{(1/3)((3*3)/5)}}}


{{{(1*3*3)/(3*5)}}}


{{{highlight(3/5)}}} bottles per minute.

This really says, or indicates  "three bottles in five minutes".  Maybe that is good enough for what he needs as his answer.  OR this common simple fraction is also  {{{3/5}}} bottles per minute  or   {{{0.6*(bottles/minute)}}}.