Whilst updating my earlier post on Water Analysis in HB

Water Analysis in HB

I discovered this useful page of numbers on the Napier City site, read on

Water Quality

The Heretaunga Plains aquifer has some of the best water in the North Island and, until recently, did not require treatment. However, a low level E.coli reading in May 2017 saw the Napier water supply chlorinated as a precautionary measure. In July 2017, an independent drinking water assessor revoked the Council’s ‘secure bore’ status, a decision that ensured chlorination had to continue. We then began extensive work on improving the safety of our bores. Prior to these improvements starting, all of our bore heads were below ground. We raised three of the 10 above ground and improved the bore chambers of others. This work was completed in December 2017. 

We carry out daily or alternate day testing on our operating bores, depending on the bore status. We also take regular samples from our reservoirs and pipe network to monitor our supply and ensure it meets the Drinking Water Standards of New Zealand 2008.

Napier has never fluoridated its water supply and there are no plans to.

Typical chemical composition of Napier water supply:

• Hardness – the sum of all calcium and magnesium compound in water results in the total hardness, measured in milligrams calcium carbonate per litre (CaCO3 mg/l). Average total hardness value for Napier water is 66 mg/l, which equals to 6.6 French degrees or 3.7 German Degrees. American Water Works Association classifies waters with up to 75 mg/l CaCO3 as soft water.
• Alkalinity – is the capacity of water to resist acidification. Napier water’s alkalinity is in range 59 – 82 mg/L CaCO3, depending on the source used.
• pH – the pH of water is a measure of the acid-base equilibrium and, in most natural waters, is controlled by the carbon dioxide-bicarbonate-carbonate equilibrium system. An increased carbon dioxide concentration will therefore lower pH, whereas a decrease will cause it to rise. The pH of most drinking-water lies within the range 6.5-8.5. Water in limestone areas such as within aquifer beneath Napier tend to have a higher pH value. Average pH of Napier reticulated water sits around 8.1.
• Total Dissolved Solids (TDS) – is a measure of the dissolved combined content of all inorganic and organic substances present. Mean TDS value in Napier reticulation is 96 mg/l.
• Nitrates – Nitrate is one of the most frequent groundwater pollutants in rural areas. The origin of nitrate is primarily from fertilizers, septic systems and manure storage or spreading operations. The Maximum Acceptable Value (MAV) in Drinking-water Standards for NZ is 11.3 mg/l, expressed as Nitrate-N. Nitrate-N levels vary across Napier bores and are in range <0.01 – 0.18 mg/l.
• Heavy metals – None of the heavy metal elements tested in our groundwater (including chromium, cadmium, mercury, lead, cobalt, nickel, copper and zinc) has ever returned above 50% of the Maximum Acceptable Value.
• Sodium, Potassium, Calcium, Magnesium and Chloride – average values in Napier reticulation for these ions are 11.4 mg/l, 1.5 mg/l, 22.0 mg/l, 2.0 mg/l and 8.1 mg/l respectively.
• Iron and Manganese – The National Drinking Water Standards set a guideline value for iron at 0.2 mg/l. Average iron concentration in Napier supply is 0.02 mg/l. The maximum acceptable value for manganese is 0.4 mg/l. Average manganese concentration in Napier supply is 0.02 mg/l.

However, if tap water is discoloured this is caused by mains maintenance or change of flow in the network. During these events, iron and manganese levels might exceed these values when sediments and deposits in the pipes are dislodged. It is the iron- and manganese-oxides that give the discoloured water distinctive reddish to blackish tint. This is why we advise not to consume discoloured water, although the concentration of manganese in such water is usually in the same magnitude range as levels found in a pineapple or an English breakfast tea.

Although our manganese levels are substantially lower than NZ’s maximum acceptable value (set based on associated public health risks), they are above the industry aesthetic value threshold of 0.01 – 0.02 mg/L. This is due to the discoloured water incidents in we’ve had in Napier’s reticulation which has occurred more frequently in recent years.

 The majority of Napier’s bores produce water with manganese below 0.002 mg/l, however two of Napier city’s bores are in 0.056-0.070 mg/l manganese range  and this causes discolouration. NCC keeps these two bores offline whenever possible, however to keep up with summer’s increased demand these are accessed to supply during the hot months. Projects to replace these two bores with low-manganese source are underway.