Operating expenses increased $5.6 million, or 13.2 percent. Brinderson added $5.9 million to operating expense. United Pipeline Systems increased operating expense by $0.4 million to support international expansion and provide additional support to the Moroccan project. Corrpro realized cost savings from ongoing initiatives to enhance sales and operational efficiencies. North American Water and Wastewater operating expenses decreased significantly as a percent of revenue because of efficiency gains achieved over the last two years through project management along with operational and administrative realignment. Operating expenses in International Water and Wastewater have been steady as new investments to improve operational management have been offset by savings from the reduced operations in Singapore and realignment of operations in certain European countries. Operating expenses as a percent of revenue for Commercial and Structural increased as a result of continued investments to build the infrastructure necessary to achieve our growth objectives.
The Company reversed a $2.8 million earnout liability in the third quarter of 2013 to reflect the high probability that CRTS will not achieve its negotiated EBITDA target in 2013 because of the delay in the Wasit project. This compares to a $6.9 million reversal in the third quarter of 2012 largely due to a previous delay in the same project. The earnout reversal in the consolidated statements of operations directly impacts the year-over-year comparison for the Energy and Mining platform.
On a non-GAAP basis, operating income decreased 11.5 percent to $24.3 million. The North American Water and Wastewater segment improved operating performance by $4.0 million, while International Water and Wastewater reduced its operating loss by $2.5 million. Offsetting the improved performance was an operating income decline in our Energy and Mining and Commercial and Structural platforms of $6.3 million and $3.4 million, respectively.
Cash FlowNet cash flow provided from continuing operations in the first nine months of 2013 was $41.6 million, or 111.5 percent of income from continuing operations, compared to $57.8 million in the first nine months of 2012. The decrease in operating cash flow from 2012 to 2013 was primarily related to slower than anticipated cash collections in the first half of the year from customer-directed project delays across several businesses and lost production days in the first half of 2013 from severe weather. We used $12.6 million of working capital during the nine-month period ended September 30, 2013 compared to $2.8 million used in the comparable period of 2012. Cash collections improved significantly in the third quarter and we expect further improvement in the fourth quarter. Also, in the first nine months of 2013, we incurred $4.2 million in acquisition-related expenses compared to $2.6 million in the first nine months of 2012.