Water in the Oil?

My boiler was working fine; this week I got an oil delivery and we felt that the heat in the radiators was not strong enough. Yesterday the boiler stopped completely. We changed the filter assuming that there are some left rabbish from the tank got into the furnace but we still have no heat. I was told by a friend that a similar problem happen to him and when he called for repairs they found water in the oil. Could this be my case? and if yes how can I repair it; I don't have a service contract and I buy my oil COD.
Thanks