While hired to perform a peer review of another assessor's recommendations, this question was asked of me. It had to do with a property damage insurance claim where an assessor had written an opinion stating that the wind driven rain, that entered the subject residence during hurricane Sally, was Category 3 water. To understand the assessor’s recommendation, one needs to have some perspective on the standards of care that governs water-damage restoration, namely the Institute of Inspection, Cleaning and Restoration Certification (IICRC) S500, Standard for Professional Water Damage Restoration. In the S500, it categorizes water-damage by whether the water is clean or contaminated. Here’s what the S500 has to say about the categories of water-damage: 

The lawyer opposing the assessor’s findings asked me if rainwater was safe to drink because the assessor failed to adequately establish the cleanliness of the water in this case. (Was the water in this building contaminated? There, simply, was no evidence to support a conclusion either way.) In her mind, it was absurd to state a water damage is “grossly contaminated” containing “pathogenic, toxigenic, or other harmful agents” that “cause serious illness… to those exposed” without proof. 

Before I continue, what’s your stand on this? Do you think wind driven rain is contaminated? 

Environmental scientists state that in most cases – before the water interacts with the ground – it is safe to drink. However, once it mixes with other things, its cleanliness depreciates. Does that mean that once rainwater enters a building’s components (e.g., insulation and drywall) it becomes Category 3 water? No. I’ve tested water in a lot of different types of buildings after various weather systems, and many are not contaminated with Category 3 water. Some are Category 3 water damage; some are Category 2; others are Category 1. 

So, what makes the difference? Why is rainwater clean in one building but “grossly contaminated” in another? It has to do with what it mixes with. I’ve seen buildings with animal feces on the floor. If the water enters and mixes with that, then, at least in that portion of the wet building, it is Category 3 water (most of the time I’ve sampled such areas). But some buildings are very new and very clean, so when the rainwater enters it does not mix with substances that contaminate it. 

BUT, what about hurricane water? Where substantial amounts of debris have been disturbed and become airborne, it is possible for the rainwater to mix with these substances and deteriorate in cleanliness. To what degree it has and what risk it poses to workers and other building occupants varies.