Understanding water damage restoration and secondary damage

Water loss events can be from many sources and the goal of this informative blog is to help you the reader understand why the source and category of water is important and understanding the potential damage and corrective actions required.

Firstly “Restoration” at its root meaning it is described as: “To return something to its nearly original state or form” or often “return to a pre-loss condition”. To provide some clarity behind the meaning of industry jargon, this is simply to return the property or possession back to the owner in the same condition or better than prior to any damage occurring.

The industry classifies restoration into 3 phases, mitigation, restoration and reconstruction. Here we will look at mitigation as this is where the focus should primarily be.

Mitigation – the action of reducing the severity, seriousness, or painfulness of something.

This is simple, the quicker action is taken the better chance the restorer has of reducing the severity or seriousness and preventing secondary damage, it is worth noting with water loss this is to be decided in minutes and hours not days and the category of water needs to be taken into account and the materials affected.


Category 1 Water – Refers to a source of water that does not pose substantial threat to humans and classified as “clean water”. Examples are broken water supply lines, tub or sink overflows or appliance malfunctions that involves water supply lines.

Category 2 Water – Refers to a source of water that contains a significant degree of chemical, biological or physical contaminants and causes discomfort or sickness when consumed or even exposed to. Known as “grey water”. This type carries micro organisms and nutrients of micro organisms. Examples are toilet bowls with urine (no faeces) and water discharge from dishwashers or washing machines.

Category 3 Water – Is known as “black water” and is grossly unsanitary. This water contains unsanitary agents, harmful bacteria and fungi, causing severe discomfort or sickness. Type 3 category is contaminated water sources that affects the indoor environment. This category includes water from sewage, seawater, rising water from rivers or streams, ground surface water or standing water.

Category 2 Water or Grey Water that is not promptly removed from the structure or has remained stagnant, may be re classified as Category 3 Water. Toilet back flows that originates from beyond the toilet trap is considered black water contamination regardless of visible content or colour.  The water category number can increase every 24 hours if left and no control measures put in place like air movement, heat and dehumidification.

Dehumidification by itself does not dry properties but is very useful in slowing down damage and preventing secondary damage from high humidity. Air movement across a surface is key to cause evaporation and speed drying.  You will note the longer water is left in or on a material, the higher the Category it becomes.  This time is subject to varying conditions in the environment such as temperature, but what is more often ignored is the age and condition of the property.

Future blogs will go deeper into drying goals and standards, but to quickly summarise, a moisture content of 16 % is desired in water loss events.  If you have built your own home or have building experience, you may know that 18% is the maximum and in some cases 20% is permitted in durable materials such as H1.2 treated timber, so why the difference.

The IICRC standard S500 for water damage restoration states 16%, as the focus is on preventing secondary damage such as mould growth. NZS3602:2003 for pre line inspections by the local council requires 18% – 20%, as this mainly refers to new builds or new building materials being installed with limited microbial of fungal conditions, when compared to a property that has been standing for several years.

With all this in mind, a simple leak from plumbing or a broken washing machine or dishwasher, can escalate easily into a category equivalent to a sewerage leak.

Mitigation is key.  A certified restorer such as NZRS can apply mitigation procedures within hours of the water loss event, preventing secondary damage and mitigating the loss.

Building Code of practice

How often do we hear the building has been built to code, meaning it is built to the minimum standard.  Wouldn’t it be nice to hear only part of the property was built to code, the remainder was built to exceed code and all the warranties of the installed materials are complete. How many building materials retain their warranty if affected by water for prolonged periods? Gib recommends 18% moisture content but Winstone Wallboards recommends a lower moisture content of 12% or less at installation so these materials can’t stand extended periods of moisture damage. 5% raise in moisture change can result in a 1mm dimensional movement in timber, this can damage materials past the point of warranty cover.


The time between the water loss event and mitigation is crucial to returning the property or possession to a pre-loss condition without the replacement of materials. Secondary damage due to moisture and mould can be reduced or even eliminated if the environment is controlled and the materials dried in the shortest time practicable. Some materials cannot be restored.

NZRS can evaluate the costs of restoration compared to replacement of the material or possession if mitigation procedures are swift.

ANSI/IICRC S520 – Mould Remediation
ANSI/IICRC S500 Water Damage Restoration
GIB – Best Practice Guidelines
NZS 3602:2003 – Timber and wood-based products for use in building