The black stains around the taps and sink are likely to be mould spores in the work top as a result of prolonged water ingress in to the wood. If left untreated, this will ultimately lead to wood rot and decay. The affected areas should be sanded back to bare wood and treated with a mould and mildew cleaner such as Barrettine Mould and Mildew Cleaner, several applications may be required if the discoloration is bad. Once fully dried the whole worktop should be treated with a worktop oil to prevent further water ingress and future mould. For additional protection, a coat of Osmo Wood Protector (4006) can be applied prior to oiling. This product offers excellent water repellency.