Flooding triggered by storms caused hundreds of millions of pounds of damage in Wales.Read more
An extra £6m has been made available to farmers affected by flooding earlier this year.
Storms Ciara and Dennis brought heavy rain to large swathes of the UK leaving thousands of acres of farmland underwater.
The National Farmers' Union said the government has now pledged £10m in total for those affected.
NFU Deputy President Stuart Roberts said the increase in funding would be a "huge relief" to farmers, some of whom are facing bills of "hundreds of thousands of pounds".
Welsh Water says sewer overflows are designed to protect homes and businesses from sewer flooding.
Speaking in Worcestershire, the PM said a visit from him during the floods would have "diverted" response teams.