Your central heating service engineer should be able to test for water and arrange for its safe removal. Testing should form part of your normal system service and should be done annually. The removal of water, or any other contamination, from an oil storage tank is a specialist task and correct disposal of the resulting waste material is controlled by environmental legislation. It isn’t something that homeowners should undertake themselves.
The principal sources of water in oil storage tanks are rainwater and condensation, with condensation being the more common. Rainwater can enter a tank if openings in the tank are left open, seals are faulty or damaged or the integrity of the tank has been compromised by rusting or by perforations, cracks or splits in the body of the tank. Condensation will often occur naturally as the result of temperature differences between the tank/oil and the surroundings.
It is most unlikely to have been delivered with the fuel. Water has a very low solubility in fuel oils and, if present in a dispersed form, would create a distinctly hazy product that would immediately fail to meet the specified criterion for the product, which is required by the British Standard to be clear and bright. Delivery tankers are not flushed with water, or water-based cleaning agents, and oil distribution facilities are fitted with high off-take points and comprehensive water trapping and filtration systems. It is part of a delivery driver’s training to ensure that all of the openings used when filling a tank and gauging its contents are closed securely after the filling operation has been completed. Also most delivery pumps will automatically shut off if water is detected.
Home owners should be aware that the Environment Agency prohibits the refilling of an oil storage tank that is damaged in such a way that it may leak or rupture after filling. Where the tank is still under warranty, the installer, or the tank manufacturer, should be informed of the nature of the failure and a claim made under the warranty.
Although a water ingress problem is unlikely to be the fault of your oil supplier, a Member of the Federation of Petroleum Suppliers will do all that is reasonable to assist you with resolving the problem and can carry out water dipping tests and water removal at your request, although a charge may have to be made for this service.