It may be a surprise but it is well known that a flooded home generally wet for more than 3 days should only be entered wearing special breathing apparatus. This current advice was originally provided by the respected building research group CIRIA as far back as 2002 and can be found on their web site (CIRIA Link) and (specific link). The advice was intended for builders and their employers who have a legal duty to protect workers from health risks under various legislation. This key advice was accepted and published with support of the Association British Insurers and Environment Agancy but unfortunately employement legislation does not cover the homeowner or tenant. Water is the single most important component of all life forms and will trigger dormant spores and amplify bacterial growth. Floodwater must be assumed to be contaminated with industrial chemicals , farm fertilisers, sewage or general pathogens from soil and sewers and can be found to contain up to 1500 viral and 120 bacterial infections.