As soon as convenient after taking possession the commission shall cause to be read all meters of consumers supplied from such waterworks. At least two days’ notice shall be given to the owner in advance of the meter reading and the owner may have a representative present at the reading. The total sum due as shown by the meter readings shall be divided in the ratio in which the period of time that has elapsed between the last preceding meter reading and the date the commission takes possession bears to the period of time that has elapsed between such date and the date of meter reading taken by the commission. The owner shall be entitled to the proportion of the total sum due that shall correspond to the period during which it had possession of the waterworks between its last previous meter reading and such date. All sums shown to be due by the meter reading by the commission shall be collected by it and the owner shall assign to it for the purpose of making such collections its proportionate interest therein as hereinbefore defined. The commission shall use all legal methods for the collection of all sums shown to be due by its meter reading and shall pay over to the owner promptly such parts of the sums of money so collected as may be due to the owner.