The shortfall reflected an increase in household revenue being offset by lower non-household revenue, due to closures at its commercial customers' operations.
The FTSE 250-listed company, however, said it is on track to deliver financial results in line with management expectations.
Expected cash and committed facilities are estimated to be “well in excess” of £3bn as of September 30, 2020, the group added.
Following the completion of the sale of Viridor in July, Pennon's debt restructuring programme is progressing, with around two-thirds repaid to date of £900mln goal.
The firm said South West Water remains on track to deliver continued Return on Regulated Equity outperformance, while the £1bn investment programme to 2025 is “well underway”.
"The group are looking at acquisitions, but not saying what those might be. They will be returning some of the money back to shareholders, but we have to wait until November to learn how they plan to do this," said Steve Clayton, manager of the HL Select UK Income Shares find.
"November’s announcement of their future plans is critical. Given management’s success to date, investors will be inclined to sit tight and wait for the news."
Pennon shares dipped 1% lower to 1,034.5p on Friday at the opening bell.