Norwegian Drinking Water Research Articles

Low levels of per- and polyfluoroalkyl substances (PFAS) detected in drinking water in Norway, but elevated concentrations found near known sources

Per- and polyfluoroalkyl substances (PFAS) are ubiquitous contaminants which are also found in drinking water. Concentration levels in drinking water vary widely and range from a very low contribution to total daily exposure for humans to being the major source of uptake of PFAS. PFAS concentrations in Norwegian drinking water has been rarely reported. We investigated concentrations of 31 PFAS in 164 water samples, representing both source water (i.e., before drinking water treatment) and finished drinking water. Samples were taken from 18 different water bodies across Norway. The 17 waterworks involved supply drinking water to 41 % of the Norwegian population. Only four of the waterworks utilised treatment involving activated carbon which was able to significantly reduce PFAS from the source water. Samples of source water from waterworks not employing activated carbon in treatment were therefore considered to represent drinking water with regards to PFAS (142 samples). All samples from one of the water bodies exceeded the environmental quality standard (EQS) for perfluorooctane sulfonic acid (PFOS) according to the water framework directive (0.65 ng/L). No concentrations exceeded the sum of (20) PFAS (100 ng/L) specified in the EU directive 2020/2184 for drinking water. Several EU countries have issued lower guidelines for the sum of the four PFAS that the European Food Safety Authority (EFSA) has established as the tolerable weekly intake (TWI) for PFOS, perfluorooctanoic acid (PFOA), perfluorononanoic acid (PFNA), and perfluorohexane sulfonic acid (PFHxS). Denmark and Sweden have guidelines specifying 2 and 4 ng/L for the sum of these PFAS. Only one of the 142 drinking water samples exceeded the Danish TWI and contained a sum of 6.6 ng/L PFAS. A population exposure model, for individuals drinking water from the investigated sources, showed that only 0.5 % of the population was receiving PFAS concentrations above the Danish limit of 2 ng/L.

Removal of a cyanotoxins mixture by loose nanofiltration membranes applied in drinking water production

Cyanobacterial toxins may threaten human health if their levels in drinking water exceed certain thresholds. Therefore, it is important for water works that use raw water sources prone to cyanobacterial blooms to have efficient barriers against such toxins. Nanofiltration (NF) is one potential barrier. The efficacy and mechanism of removing four cyanotoxins, namely microcystins (MCs), cylindrospermopsin (CYN), saxitoxins (STXs), and anatoxin (ATX), were studied at bench-scale using NF membranes commonly applied in Norwegian drinking water facilities. The average removal of the different cyanotoxins under the tested operating conditions ranged from 15 % to 96 %. The membrane with the lowest molecular weight cut-off (MWCO) of 0.3 kDa made of polyamide (PA) was deemed the most suitable for the removal of all studied cyanotoxins. A gradual improvement of rejection observed with the 2 kDa cellulose acetate (CA) membrane was linked to the formation of fouling on the membrane surface. Sulfonated polyethersulfone (SPES) membranes with MWCO of 1 and 3 kDa could not efficiently and consistently remove cyanotoxins, except for MCs. The rejection of MCs over time was over 80 % by the SPES membranes during two days of filtration. The influence of pressure and pH as relevant operating parameters was evaluated. However, the analysis of the cyanotoxin concentrations in the permeate indicated that the investigated NF membranes alone would generally not be able to meet the WHO guidelines for drinking water during a severe cyanobacterial bloom. Thus, incorporating other water treatment technologies should be considered to effectively remove cyanotoxins.

Uranium and lanthanum in Norwegian drinking water – Is there cause for concern?

Due to natural conditions such as geology, topography, and climate, and historical features such as resource utilization, land use, and settlement patterns, the drinking water supply in Norway is separated into many public and private water supply systems. This survey sheds light on whether the Drinking Water Regulation's limit values provide a sufficient basis for ensuring safe drinking water for the Norwegian population. Participating waterworks, both private and public, were spread throughout the country, in 21 municipalities with different geological conditions. The median value for the number of persons supplied by the participating waterworks was 155. The two largest waterworks, both of which supply >10,000 people, have water sources from unconsolidated surficial sediments of latest Quaternary age. Fourteen waterworks have water sources from bedrock aquifers. Raw and treated water were analysed for 64 elements and selected anions. The concentration of manganese, iron, arsenic, aluminium, uranium, and fluoride exceeded the respective drinking water regulations' parametric value given in Directive (EU) 2020/2184. Regarding the rare earth elements, neither WHO, EU, USA nor Canada have established any limit values. However, concentration of lanthanum in groundwater from a sedimentary well exceeded the health-based guideline value that applies in Australia. Results from this study raise the question of whether increased precipitation can have an impact on the mobility and concentration of uranium in groundwater from bedrock aquifers. Furthermore, findings of high levels of lanthanum in groundwater create uncertainty as to whether the current quality control of Norwegian drinking water is sufficient.

Variation of Legionella spp. with Lake Depth and Season in Two Norwegian Drinking Water Sources

In Norway, placement of the water treatment plant intake within the lake hypolimnion is considered a hygienic barrier against pathogens of fecal origin. It is unclear, however, whether this practice provides a barrier against opportunistic pathogens such as Legionella. In this study, water samples were collected at 10 m depth intervals near the drinking water intakes of two lakes. Legionella and one of their common hosts, Acanthamoeba spp., were quantified using culture-based assays (Legionella pneumophila only) and real-time quantitative PCR (qPCR). L. pneumophila and Acanthamoeba spp. were never detected by qPCR; Legionella spp., however, were present in all samples at concentrations ranging from 2.33 to 4.14 log10[copies/L] in lake A and from 2.69 to 4.27 log10[copies/L] in lake B. For most sampling months in both lakes, there was no significant difference between total bacteria and Legionella spp. concentrations at the intake depth versus those on the lake surface. The results of this limited investigation of two Norwegian water supplies suggest that placement of water treatment plant intakes within the hypolimnion may not afford a sufficient hygienic barrier against Legionella.

A nature-based solution to a landfill-leachate contamination of a confined aquifer

Remediation of groundwater from landfill contamination presents a serious challenge due to the complex mixture of contaminants discharged from landfills. Here, we show the significance of a nature-based solution to a landfill-contaminated aquifer in southeast Norway. Groundwater physicochemical parameters monitored for twenty-eight years were used as a proxy to infer natural remediation. Results show that concentrations of the major chemical variables decreased with time and distance until they tailed off. An exception to this was sulphate, which showed an increase, but apparently, exhibits a stationary phase. The water types were found to be most similar between samples from active landfill and post-closure stages, while samples from the stabilised stage showed a different water type. All the chemical parameters of samples from the stabilised stage were found to be within the Norwegian drinking water standards, except iron and manganese, which were only marginally above the limits, an indication of a possible recovery of this aquifer. The findings highlight the significance of natural attenuation processes in remediating contaminated aquifers and have significant consequences for future contamination management, where natural remediation can be viewed as an alternative worth exploring. This is promising in the wake of calls for sustainable remediation management strategies.

Risk assessment of parasites in Norwegian drinking water: opportunities and challenges

Despite the relative prosperity of Scandinavian countries, contamination of the drinking water supply with parasites has occurred on various occasions in the last few decades. These events have resulted in outbreaks of disease involving several thousand cases and/or the necessity for implementation of boil-water advisories. Against this background, in 2008, and again in 2019, the Norwegian Food Safety Authority requested a risk assessment from an independent scientific body regarding parasites in Norwegian drinking water. On each occasion, it was requested that specific questions were addressed.For the first assessment, data, both of general relevance and specific for Norway, were collected from appropriate sources, as available. Based on some of this information, a quantitative probability model was established and run to estimate the number of cases of waterborne cryptosporidiosis and giardiasis that may be expected in Norway, both in the general public and the immunocompromised, and under conditions where water treatment should be optimal, and also when water treatment efficacy may be compromised by weather conditions.For the second assessment, approximately a decade after the first, an update on the previous assessment was requested. Differences in information availability and other changes between the two assessments were described; although more data were available at the second assessment, considerable gaps still remained. For both assessments, data on the occurrence of these parasites in the Norwegian population, particularly those infected in Norway, were considered a challenge. However, due to changes in reporting requirements in 2020, the situation was improved for the second assessment. In addition, data were lacking for both assessments on whether animals or humans are most likely to contaminate water sources, and the species and genotypes of these parasites in Norwegian animals. It was also noted that some of the newer data on parasite numbers detected in water samples should be treated with caution. Due to this, further modelling was not conducted. The relevance of risk-based sampling rather than ad hoc sampling of water sources was also addressed.Despite the data gaps, this article provides an overview of the opportunities provided by conducting such assessments. In addition, some of the challenges encountered in attempting to estimate the risk posed from parasite contamination of water sources in Norway, particularly under predicted conditions of climate change, are described.

Long-term redox conditions in a landfill-leachate-contaminated groundwater

Indicators of redox conditions; oxygen, sulphate, nitrate, ammonium, iron and manganese, and in addition, bicarbonate and total organic carbon were studied in groundwater samples contaminated by leachate emanating from Revdalen Landfill (Norway). Based on these variables, the study aimed to deduce the redox conditions in the aquifer. Literature on landfill leachate contamination of confined aquifers is scarce and to the best of our knowledge, this study, which describes long-term analysis of redox chemistry, is the first of its kind in such an environment. Groundwater samples were monitored for a period of 24 years, enabling us to describe redox conditions on both short-term and long-term bases. Levels of measured parameters in the contaminated aquifer varied spatially and with time, but were generally elevated except oxygen; pH (4.9–8.8), oxygen (0–11.3 mg/L), sulphate (0–28 mg/L), nitrate (0–16 mg N/L), ammonium (0.02–40 mg/L), iron (0–99 mg/L), manganese (0.06–16 mg/L), bicarbonate (22–616 mg/L) and total organic carbon (1.3–47 mg/L). From the result, levels of iron, manganese, nitrate and ammonium violated the Norwegian drinking water norms. However, iron, ammonium, total organic carbon and bicarbonate showed strong attenuation along the groundwater flow path. By contrast, oxygen, nitrate and sulphate increased farther out in the plume. The redox conditions that developed in the aquifer were similar to those previously reported for phreatic aquifers, structuring by proximity to the landfill as sulphate-reducing, iron-reducing, manganese-reducing, nitrate-reducing, and finally aerobic condition. Eventually, there was an apparent breakdown of this system due to ecosystem shift in the landfill when leachable reduced ions were depleted and the landfill became aerobic. Overall, the redox framework provided remarkable attenuation to contaminants, and thus prevented potential degradation of ecological health due to the landfill leachate.

Detection of Aminoglycoside Resistant Bacteria in Sludge Samples From Norwegian Drinking Water Treatment Plants.

Through a culture-based approach using sludge from drinking water treatment plants, this study reports on the presence of aminoglycoside resistant bacteria at 23 different geographical locations in Norway. Sludge samples are derived from a large environmental area including drinking water sources and their surrounding catchment areas. Aminoglycoside resistant bacteria were detected at 18 of the sample sites. Only five samples did not show any growth of isolates resistant to the selected aminoglycosides, kanamycin and gentamycin. There was a statistically significant correlation between the numbers of kanamycin and gentamycin resistant bacteria isolated from the 23 samples, perhaps suggesting common determinants of resistance. Based on 16S rRNA sequencing of 223 aminoglycoside resistant isolates, three different genera of Bacteroidetes were found to dominate across samples. These were Flavobacterium, Mucilaginibacter and Pedobacter. Further phenotypic and genotypic analyses showed that efflux pumps, reduced membrane permeability and four assayed genes coding for aminoglycoside modifying enzymes AAC(6′)-Ib, AAC(3′)-II, APH(3′)-II, APH(3′)-III, could only explain the resistance of a few of the isolates selected for testing. aph(3′)-II was detected in 1.6% of total isolates, aac(6′)-Ib and aph(3′)-III in 0.8%, while aac(3′)-II was not detected in any of the isolates. The isolates, for which potential resistance mechanisms were found, represented 13 different genera suggesting that aminoglycoside resistance is widespread in bacterial genera indigenous to sludge. The present study suggests that aminoglycoside resistant bacteria are present in Norwegian environments with limited anthropogenic exposures. However, the resistance mechanisms remain largely unknown, and further analyses, including culture-independent methods, could be performed to investigate other potential resistance mechanisms. This is, to our knowledge, the first large scale nationwide investigation of aminoglycoside resistance in the Norwegian environment.

Use of lectin-magnetic separation (LMS) for detecting Toxoplasma gondii oocysts in environmental water samples

Proof-of-principle of lectin-magnetic separation (LMS) for isolating Toxoplasma oocysts (pre-treated with 0.5% acidified pepsin (AP)) from water for subsequent detection by microscopy or molecular methods has been shown. However, application of this technique in the routine water-analysis laboratory requires that the method is tested, modified, and optimized.The current study describes attempts to apply the LMS technique on supernatants from water samples previously analyzed for contamination with Cryptosporidium and Giardia using standard methods, and the supernatant following immunomagnetic separation (IMS) retained.Experiments on AP-treatment of Toxoplasma oocysts in situ in such samples demonstrated that overnight incubation at 37 °C was adequate, but excess AP had to be removed before continuing to LMS; neutralization in sodium hydroxide and a single wash step was found to be suitable. Mucilaginous material in post-IMS samples that had been stored at room temperature without washing, which was found to be probably an exudate from bacterial and fungal overgrowth, hampered the isolation of T. gondii oocysts by LMS beads.For detection, microscopy was successful only for clean samples, as debris occluded viewing in dirtier samples. Although qPCR was successful, for some samples non-specific inhibition occurred, as demonstrated by inhibition of an internal amplification control in the qPCR reaction. For some, but not all, samples this could be addressed by dilution. Finally, the optimized methodology was used for a pilot project in which 23 post-IMS water sample concentrates were analyzed. Of these, only 20 provided interpretable results (without qPCR inhibition) of which one sample was positive, and confirmed by sequencing of PCR product, indicating that Toxoplasma oocysts occur in Norwegian drinking water samples.In conclusion, we suggest that post-IMS samples may be suitable for analysis for Toxoplasma oocysts using LMS, only if freshly processed or washed before being refrigerated. In addition, application of AP treatment requires a neutralization step before proceeding to LMS. For detection, qPCR, rather than microscopy, is the most appropriate approach, although some inhibition may still occur, and therefore inclusion of an internal amplification control is important. Our study indicates that, despite some limitations, this approach would be appropriate for further large-scale analysis of samples of raw and treated drinking water.

No simple solution to waterborne fungi: various responses to water disinfection methods

Control strategies against waterborne fungi have been studied only to a small degree. In order to increase knowledge of the effect of water treatment on waterborne fungi, the dose–response effect of four commonly used drinking water disinfection methods was tested on selected fungal species: Aspergillus calidoustus, Penicillium spinulosum, Trichoderma viride and Fusarium solani. These species are all common in Norwegian drinking water, and are regarded as emerging pathogens, toxigenic and/or food contaminants. Spore suspensions were treated with ultraviolet (UV) irradiation, ozone, chlorine and chloramine. Three different doses were tested for each disinfectant and all doses were repeated three times. Bacillus subtilis was included as a control for the disinfection processes and to compare the resistance. P. spinulosum and T. viride were resistant to chlorine and chloramine. They were also very tolerant to UV-irradiation and ozone, although the highest doses of ozone had a small inactivation effect, especially on T. viride. Ozone was found to be most effective against fungi in general. It is apparent that fungal species may have very different properties when it comes to tolerance to water disinfection, and the inactivation of B. subtilis spores cannot be used as an indicator of fungal spore inactivation after water treatment.

Environmental analysis of chemicals and energy consumption in water treatment plants: case study of Oslo, Norway

This paper studies the trend in the consumption of energy and chemicals and the associated environmental impacts, for water treatment plants (WTPs) in Oslo, over the years between 2000 and 2009. The Norwegian Drinking Water Regulations stipulate that supplied water should comply with over 50 quality criteria. Abiding by the regulations and improving the water quality has its costs – economically and environmentally. Quality improvement entails, inter alia, the consumption of more chemicals, both in terms of quantity and variety, and a rise in energy consumption. In order to determine the environmental impacts of the consumption of chemicals and energy, an environmental life cycle assessment (LCA) was carried out. It was observed that the impacts of chemicals have increased dramatically after 2007, courtesy of a process upgrading at one of the WTPs. Except in the years 2004 and 2007, the impacts attributable to chemicals consumption have exceeded those due to energy consumption. Global warming is the key impact in both cases, though in the case of energy consumption, abiotic depletion and acidification are also significant.

Exploring the species diversity of Trichoderma in Norwegian drinking water systems by DNA barcoding

A total of 123 Trichoderma strains were isolated from Norwegian surface-sourced drinking water. The water samples included raw water, treated water, and water from private homes and hospital installations. Trichoderma species are difficult to differentiate morphologically, but recent molecular identification tools, including DNA barcoding, successfully distinguish between closely related species. The diversity of Trichoderma spp. was explored by DNA sequencing of internal transcribed spacer (ITS) and translation elongation factor 1 alpha (TEF-1α). Sequence identification was performed in the TrichOKEY version 2.0 barcode program and in the multilocus similarity search database TrichoBLAST, combined with traditional blast searches in the EMBL/GenBank. A total of 11 known Trichoderma/Hypocrea species were identified. In addition, one group of unidentified Trichoderma strains was found to represent a separate, strongly supported subclade within the Pachybasium'A'/Hamatum clade, based on their TEF-1α haplotypes. Trichoderma viride comprised 49% of the identified strains, and was represented by four and eight slightly different ITS and TEF-1α haplotypes, respectively. Approximately 22% of the surface-derived water samples were positive for T. viride, and the species was frequently isolated throughout the surface-sourced drinking water distribution system. The results indicate that a broad range of Trichoderma species are present in Norwegian surface-sourced drinking. Water treatment has minor effect in removing Trichoderma from raw water, and active growth in the water distribution system is likely to occur.

A water contamination incident in Oslo, Norway during October 2007; a basis for discussion of boil-water notices and the potential for post-treatment contamination of drinking water supplies

Over a 5 day period in October 2007 a boil-water notice was served on the majority of Oslo, capital city of Norway, as a result of a combination of bacteriological findings (coliforms, intestinal enterococci, and E. coli), and very low numbers of Cryptosporidium oocysts and Giardia cysts in 10 L water samples taken from the water distribution network. The water source had been regularly monitored for these parasites and generally found to be negative. Over 460,000 residents were affected by the boil-water notice, as were many thousands of businesses. Despite an extensive outbreak of waterborne giardiasis in Bergen, Norway during 2004/2005, occurrence of parasites in Norwegian drinking water supplies has apparently continued to be considered to be of minimal relevance by Norwegian health authorities. Here we describe the background and occurrence of the episode in Oslo, including the species of Cryptosporidium detected, and use this event, in conjunction with incidents from other countries, as a basis to discuss the following issues: (1) under which circumstances should the occurrence of Cryptosporidium oocysts and Giardia cysts in water supplies trigger the issue of a boil-water notice, and (2) the possibilities and probabilities of post-treatment contamination events in the water distribution network.

Diversity and Significance of Mold Species in Norwegian Drinking Water

In order to determine the occurrence, distribution, and significance of mold species in groundwater- and surface water-derived drinking water in Norway, molds isolated from 273 water samples were identified. Samples of raw water, treated water, and water from private homes and hospital installations were analyzed by incubation of 100-ml membrane-filtered samples on dichloran-18% glycerol agar. The total count (number of CFU per 100 ml) of fungal species and the species diversity within each sample were determined. The identification of mold species was based on morphological and molecular methods. In total, 94 mold species belonging to 30 genera were identified. The mycobiota was dominated by species of Penicillium, Trichoderma, and Aspergillus, with some of them occurring throughout the drinking water system. Several of the same species as isolated from water may have the potential to cause allergic reactions or disease in humans. Other species are common contaminants of food and beverages, and some may cause unwanted changes in the taste or smell of water. The present results indicate that the mycobiota of water should be considered when the microbiological safety and quality of drinking water are assessed. In fact, molds in drinking water should possibly be included in the Norwegian water supply and drinking water regulations.

Foetal growth and duration of gestation relative to water chlorination

OBJECTIVETo assess the effect of exposure to chlorination byproducts during pregnancy on foetal growth and duration of pregnancy.METHODSA population based study was conducted of 137 145 Norwegian children born alive...

Assimilable organic carbon and biodegradable dissolved organic carbon in Norwegian raw and drinking waters

Assimilable organic carbon (AOC) and biodegradable dissolved organic carbon (BDOC) were measured in Norwegian raw and drinking waters. Several of the water-works investigated produce a drinking water which is, or approximates to, biological stability according to the AOC analysis. The reduction of AOC by water treatment was shown to be a function of the raw water quality and the particular treatment process. Levels of AOC were generally low in Norwegian raw and drinking waters, and thus the situation appears promising with respect to controlling microbial aftergrowth during distribution. Coagulation-filtration (mainly direct filtration) trains and anionic exchange achieved significant reductions in AOC, whereas membrane filtration had little effect. Treatment plants using limited or no specific measures for removal of dissolved organic carbon (DOC) and postchlorination, increased AOC levels. Disinfection with UV light may produce less AOC than chlorination. BDOC was effectively reduced by all water treatments. Membrane filtration performed at least as well as other treatments in removing BDOC. This suggests that bulk BDOC is typically of higher molecular weight than AOC. Correlations between AOC and BDOC in raw and drinking waters were not significant. This finding supports the contention that these parameters are independent measures of the labile organic fraction of natural waters. It seems likely that the AOC and BDOC analyses target different fractions of the biodegradable organic material (BOM). When AOC and BDOC were used to evaluate the effectiveness of treatment processes the results were more promising. Correlation factors showed that these parameters generally provided complementary information about the fate of BOM during water treatment. However, because BDOC decreased during water treatment at all but one plant, whereas AOC often increased, necessitates that the raw data and the correlation factors be presented together in studies of this nature. The addition of nutrient salts in the AOC assay usually gave moderate increases in the values obtained. Consequently, nutrients other than organic carbon may limit aftergrowth in Norwegian drinking water. Use of an alternative bioassay organism gave lower AOC values, thus confirming the suitability of the standard assay organism.

The chemistry of Norwegian groundwaters: III. The distribution of trace elements in 476 crystalline bedrock groundwaters, as analysed by ICP-MS techniques

Four hundred and seventy-six groundwater samples from boreholes in Norwegian crystalline bedrock have been analysed by ICP-MS techniques. The results for 53 trace elements are presented as cumulative frequency distribution diagrams and are compared with relevant international drinking water norms. A range of trace elements appear to be enriched in granitic waters and depleted in anorthositic waters which is to be expected as generally granitic rocks are enriched in trace elements above those in anorthosites. A selection of elements which may be toxic in excess when present in drinking water are further discussed (Be, Tl, Th, U, Cd, Pb, As, Ni, and Hg). For uranium, 18% of the samples exceed the American maximum admissible concentration of 20 μg/l; 7% of the samples fail to meet the Russian drinking water norms for beryllium of 0.2 μg/l. For some parameters such as U, Be and Tl, no Norwegian drinking water regulations are set, while the American and the Russian norms differ significantly from each other. Between 0 and 1.5% of the wells exceed Norwegian drinking water norms for each of the other selected elements.

Chemical composition of hard- and softrock groundwaters from central Norway with special consideration of fluoride and Norwegian drinking water limits: O. M. Saether, C. Reimann, B. O. Hilmo & E. Taushani, Environmental Geology, 26(3), 1995, pp 147–156

Chemical composition of hard- and softrock groundwaters from central Norway with special consideration of fluoride and Norwegian drinking water limits: O. M. Saether, C. Reimann, B. O. Hilmo & E. Taushani, Environmental Geology, 26(3), 1995, pp 147–156

Chemical composition of hard- and softrock groundwaters from central Norway with special consideration of fluoride and Norwegian drinking water limits

Groundwaters from crystalline and metamorphic rocks (hardrocks) and from Quaternary deposits, i.e., alluvial and glacial deposits (softrocks) from the counties of Nord-Trondelag and Sor-Trondelag were analyzed for major and minor elements and ions including fluoride. The median concentration of F− in water from the hardrock aquifers is 0.28 mg/l (14.7 μeq/l) in contrast to water from softrock aquifers in which it is found to be 0.05 mg/1 (2.6 μeq/l). More importantly, ca. 15% of the locations where water was abstracted from hardrock wells contain 1.5 mg/l (78.9 μeq/l) F− or more. Thus, 15% of all hardrock wells returned F− results that are at or above the maximum recommended value for drinking water. Of the softrock wells, none are above 1 mg/l. Geologists would normally expect higher F−contents in groundwaters derived from acid rocks, e.g., in granitic or gneissic areas. When comparing the host lithology with the observed F−contents, however, no clear relationship between F− content and lithology is visible. The highest observed F− values actually occur in gneissic host rocks. However, wells drilled in amphibolites/greenstones, mica schists, calcareous rocks, and sedimentary rocks all returned some analytical results above 1.5 mg/l F−. These results suggest that all hardrock wells drilled should be tested for F− and the users informed about the results and advised to take any necessary precautions. When applying the recently proposed Norwegian drinking water limits to our data, 51% of all softrock well waters and 56% of all hardrock well waters are unfit for consumption without prior treatment, although we analyzed only for about half of the proposed elements/parameters. This result seriously questions the concept of fixed action levels—many of them with totally unproven health implications—for so many parameters/elements for hardrock groundwaters.

Trace metals in Norwegian drinking water sources

(1991). Trace metals in Norwegian drinking water sources. SIL Proceedings, 1922-2010: Vol. 24, No. 4, pp. 2180-2184.