In the water

Bacteria are small single-celled organisms. Some bacteria found in water can make people sick. Drinking water treatment is designed to remove, kill or inactivate these bacteria. Drinking water suppliers are required to test for E. coli and total coliforms. E. coli indicates the presence of faecal contamination and likely presence of pathogens. Total coliform are a wider group of bacteria widely found in the environment. 

Boron occurs naturally in some groundwater. It can also come from human activities, particularly wastewater discharges.  It is hard to remove boron from water, so if there’s too much boron in a water source it may be necessary to find a new source. 

The maximum acceptable value (MAV) for boron is 2.4mg per litre of drinking water. This is based on health impacts on animals. This is a long-term MAV and set at a level to ensure boron levels in drinking water won’t pose a significant health risk over a lifetime (70 years). For this reason, short-term exposure to water with boron levels above the MAV is not generally a risk to health. 

Cadmium most commonly enters drinking water from impurities in zinc in galvanised pipes, solders and some metal fittings in distribution and plumbing systems. If cadmium is ingested in large enough quantities, it can accumulate in the kidneys.

The maximum acceptable value (MAV) for cadmium is 0.004mg per litre of drinking water. This is a long-term MAV and set at a level to ensure cadmium levels in drinking water won’t pose a significant health risk over a lifetime (70 years). For this reason, short-term exposure to water with boron levels above the MAV is not generally a risk to health.

Chlorate is one of the chemicals known as a disinfection by-product (DPB). It can occur when disinfectants such as sodium hypochlorite are used in water treatments. Levels of chlorate can normally be kept low by managing chemicals properly. There is currently no clear evidence of harm to human health. Disinfection should never be compromised to manage high chlorate levels. 

Copper is not generally a concern in water supplies in New Zealand. However, copper can enter drinking water from copper pipes and home plumbing and people should run the tap in the morning to dispose of water that has been sitting in contact with the plumbing.

While it is an essential nutrient, in large doses, copper can cause acute gastrointestinal (gut) health issues.

The maximum acceptable value (MAV) for copper is 2mg per litre of drinking water. This is a long-term MAV and set at a level to ensure copper levels in drinking water won’t pose a significant health risk over a lifetime (70 years). For this reason, short-term exposure to water with copper levels above the MAV is not generally a risk to health. 

Cyanobacteria, also called blue-green algae, are microorganisms that grow using light and are found in surface water sources. Some cyanobacteria can produce cyanotoxins that can be dangerous to humans and animals when consumed. These are difficult to remove from water, therefore suppliers must understand cyanobacteria risks in the source waters they use. If a drinking water supply is affected by cyanotoxins, immediate action may be needed to protect public health such as issuing a do not drink or do not use advisory.  

Escherichia coli, or E. coli, is a type of bacteria found in the intestines and faeces (poo) of people, other mammals and birds. It is an indicator of faecal contamination. This is important as most human pathogens in drinking water are transmitted through faecal contamination. When E. coli is detected, suppliers must take steps to manage the risk. This usually means that suppliers need to issue a boil water advisory to people using the supply. 

Iron is a naturally occurring mineral that is found in many sources of drinking water. It is generally not a health concern but can cause aesthetic issues, giving water a metallic taste and causing stains on tubs, showers, toilets, plumbing fixtures and laundry. Elevated levels of iron can also impact the efficiency of UV treatment systems, reducing the amount of UV light that is able to pass through the water (the UVT).

Lead is a metal that has been used widely in plumbing and a range of other common household substances, such as paint products, ceramics, petrol, batteries, electronics, ammunition and cosmetics. Lead is also present naturally in soils and rocks at low levels. 

Manganese is a naturally occurring mineral found in many surface drinking water sources. While it is an essential mineral, too much manganese can negatively affect human health. It can also affect the efficiency of UV treatment systems, reducing the amount of UV light that is able to pass through the water. 

Manganese can also cause aesthetic issues in drinking water such as a metallic taste and black stains on tubs, showers, toilets, plumbing fixtures and laundry/washing.

The maximum acceptable value (MAV) for manganese is 0.4mg per litre of drinking water. This is a long-term MAV and set at a level to ensure manganese levels in drinking water won’t pose a significant health risk over a lifetime (70 years). For this reason, short-term exposure to water with manganese levels above the MAV is not generally a risk to health. 

Find out more about manganese. 

Microbiological content is a measure of what, and how many, microorganisms (tiny living things) are present in a water supply.

Microorganisms are tiny living things that can’t be seen by the naked eye. They include bacteria, viruses and protozoa. While not all microorganisms are harmful when drunk, some are. These are called pathogens. The main purpose of drinking water treatment is to kill, remove or inactivate pathogens with disinfectants like chlorine and UV treatment. Testing for bacteria is important. The presence of bacteria means that treatment has not been effective or that treated water has been contaminated. 

Nitrate is a naturally occurring chemical and essential for life. It is often found at low levels in surface and groundwater however human activities such as farming and wastewater discharges can increase the levels. 

High levels of nitrate can cause a serious health condition called Methaemoglobinaemia which affects the ability of the blood to carry oxygen. The most vulnerable group is bottle-fed infants, and the condition is often called blue baby syndrome. 

The maximum acceptable value (MAV) for nitrate is 50mg per litre (or 11.3mg per litre when expressed as NO₃-N) of drinking water. This is a short-term MAV designed to protect again blue baby syndrome. If the nitrate level exceeds the MAV a do not drink advisory should be issued.

Protozoa are small single-celled parasites. Some, like cryptosporidium or giardia, can cause illness. They are excreted in faeces (poos) from animals and humans and enter the source water through run off and discharges. Protozoa are more resistant to chlorine than other microorganisms and treatment normally involves removal through suitable filters and inactivation using UV light. 

Total coliforms are a broad category of bacteria that can be found in faeces but also live in the wider environment including in soil and plants. While they do not generally pose a direct health risk, if total coliforms are found in a water sample, it indicates that bacteria are present in the water and may indicate that treatment has not been effective or that treated water is vulnerable to contamination. Drinking water suppliers are required to test for total coliforms and E. coli. E. coli is a coliform so if a sample tests positive for E. coli it will also be positive for total coliforms.