Introduction

Water plays an essential role in many religions, with sacred wells and springs being found in all the inhabited continents (e.g. Ray 2020). In Asia, these include Dragon wells in China and the Yaksutŏ mineral springs in Korea, whilst in Saudi Arabia, the Zamzam well in Mecca is probably the most important well in Islam (Ghabin 2020). There are sacred springs associated with Native American cultures, including caves and springs venerated by the Mayan people in Mexico (Dunning 2020). Snake-like water beings that bring water and life are still central to the beliefs of many indigenous communities, including those in Australia (Strang 2023). In Europe, there are numerous springs and wells named after Christian saints. A common feature of many of these sacred waters is their reputation for healing ailments. Owing to their wide occurrence and importance in religious beliefs and practices, sacred wells and springs are recognised in the groundwater-themed 2022 UN World Water Development report as providing important cultural services, along with mineral waters and hot springs (UN Water 2022). In this essay, the scientific knowledge system of hydrogeology is considered as well as a knowledge system represented by commonly held beliefs in the origins and power of water.

Whereas mineral and thermal waters (including spa sites) have received a lot of attention in the hydrogeological literature (e.g. Banks 1997; LaMoreaux and Tanner 2001; Kim et al. 2005; Baiocchi et al. 2013; Mather 2013; Lazzerini and Cardosa da Silva 2020), sacred wells less so. Some of the publications on the hydrogeology of sacred wells and springs focus on specific examples, such as two springs dedicated to St Olaf in Telemark County in Norway (Klempe 2015) or wells and springs in a particular region, such as the North Podlasie region in Poland (Jekatierynczuk-Rudczyk 2020). An article by Mather (2016) considers the distribution of sacred wells in England and Wales by region and broad geological settings. Other papers are mainly concerned with the water quality of sacred wells and springs, including holy springs in Austria (Kirschner et al. 2012) and springs in Tigray, Ethiopia (Berhe et al. 2023).

Although sacred wells occur in most countries, Ireland is unusual in having so many. Mapping in the nineteenth century recorded some 3,000 sacred wells and springs (usually referred to as holy wells, or tobair naofa in Irish) in what is now the Republic of Ireland. Although many holy wells have been lost to development or covered over and are inaccessible, others are still visited regularly, especially on the day of the saint associated with each well (known as the patron or pattern day). Beliefs in their curative powers persist among many pilgrims to these wells. Some of the wells probably date from early Christian, or even pre-Christian times, whilst others are more recent.

Because of their wide distribution and ongoing cultural importance, the holy wells in Ireland provide an excellent basis for a countrywide investigation of their hydrogeological settings and water chemistry (Misstear 2023). A 5-year study (2015–2020) involved an analysis of the distribution of the mapped holy wells according to their physiographic setting, geology, main lithology, aquifer type and groundwater vulnerability. This GIS-based analysis was followed up by field surveys of 215 holy wells, 167 of which were sampled for their chemical properties, including major ions and trace elements. This may be the most extensive hydrogeological study of holy wells carried out anywhere and, therefore, is a good basis for providing insights into sacred wells and springs more generally.

Hydrogeological settings

Details of the Irish study are published in Misstear (2023), and only key findings will be discussed here. By way of context, the bedrock geology of the Republic of Ireland (hereafter referred to as Ireland) mainly comprises Precambrian and Lower Palaeozoic metasediments and igneous rocks, overlain by Devonian sandstones and Carboniferous limestones and shales. These are mainly characterised by low permeability fractured rock aquifers, with the best (most productive) aquifers being found in the limestones which are often karstified (Drew 2018). A covering of glacial deposits includes some sand and gravel aquifers, but the presence of tills is also an important determinant regarding groundwater vulnerability classification (Misstear et al. 2009). For ease of analysis, including hydrochemical characterisation, the many different geological formations can be grouped into six main lithological groups (Tedd et al. 2017; Misstear 2023).

The GIS analysis of the full database (specifically, 2,676 holy wells with grid references) showed that Irish holy wells are found in all the main lithological groups. Moreover, their frequency of occurrence is in approximate proportion to the areas occupied by those lithologies—for example, 27% of the wells are located in pure limestones, which cover ~24% of the area of the country, and include many of the karst aquifers. In contrast, 18% of wells are in metamorphic rocks that are found across 22% of the landscape. When it comes to aquifer category, 68% of the wells are in aquifers that are classed as “poorly productive”, which underlie about 72% of the country. This implies that holy wells are nearly as common in these poor aquifers as in the more productive aquifers. Field surveys confirmed these findings, and indicated that most holy wells were created around springs and seepages, or where the water table was shallow and could be easily accessed, and that their sites represent a wide range of rock and soil types. There are only a few examples of large springs that are designated as holy wells (these are in karst limestones) and also only a small number of holy wells with their groundwater source in deep confined aquifers.

Interestingly, the study by Mather (2016) of holy (sacred) wells in parts of Britain found that they are most common in the southwest of England and in Wales, where older igneous, metamorphic and sedimentary rocks dominate (he refers to this geology as basement and older cover). Mather argues that the higher densities of holy wells in these areas of poorly permeable fractured rocks are due to groundwater being scarcer in such areas and, hence, more likely to have been venerated than in regions underlain by the main aquifers of the country, namely the Permo-Triassic sandstones and Cretaceous chalk of central and eastern England. However, given the findings from the Irish study, with holy wells also being common in areas of older rocks, other explanations are possible for the larger numbers of holy wells in southwest England and Wales: groundwater flow paths in basement aquifers are likely to be shorter than those in the more productive sandstone and chalk aquifers, leading to more (albeit small) springs and seeps; there may be greater survival rates for holy wells in the less urbanised and less intensive agricultural areas of the west and southwest; and/or that Celtic and Medieval traditions around holy wells may have persisted longer in Cornwall and Wales.

Other case studies also show a diverse range of hydrogeological settings for sacred springs and wells. In Illinois in the US there are thousands of springs in a wide variety of hydrogeological settings, from fractured bedrock to glacial deposits. Some of these springs were considered sacred by Native Americans (Swanson 2013). The two wells described in Telemark County in Norway (Klempe 2015) and the springs and wells in the North Podlasie region of Poland are associated with Quaternary aquifers (Jekatierynczuk-Rudczyk 2020); the Zamzam well in Mecca is constructed in wadi alluvium and diorite bedrock (Shomar 2012); and the sacred Wakutamaike spring in Japan issues from basaltic aquifers beneath Mount Fuji (Schilling et al. 2023).

An important finding from the research in Ireland is that the majority of holy wells are in areas where the groundwater vulnerability is classified as ‘extreme’, with bedrock within 3 m of the land surface, or ‘high’, where a protective subsoil cover above the bedrock aquifer is usually less than 5 m (Misstear et al. 2009)—74% of the mapped wells and springs were in these extreme and high vulnerability categories.

Water quality

The chemical results from the sampling of 167 holy wells in Ireland generally showed the expected hydrochemical characteristics in relation to aquifer lithology and location (Misstear 2023). Most of the groundwaters were dominated by calcium and bicarbonate ions, with harder waters in the limestones than in the noncalcareous sediments or igneous and metamorphic rocks. Well waters in upland areas were less mineralised than those near the coast, where the influence of sea spray on rainfall and, hence groundwater recharge, could be detected. In a couple of cases, shoreline wells were directly affected by inundation of the sea at high tides. Unlike some spa wells, most of the holy well samples were not highly mineralised (with median EC = 516 µS/cm) or sulphur rich (median sulphate = 10.5 mg/L). Of most interest in terms of water quality, 52% of samples had nitrate values above the Irish national background level of 8.7 mg NO3/L (Tedd et al. 2017), although only samples from three wells exceeded the drinking water limit value of 50 mg NO3/L. The large number of samples above the background level does suggest some anthropogenic influences, however. Most of these wells are in rural areas, where agriculture and waste disposal are possible sources of nitrate.

In the North Podlasie region of Poland, the holy springs and wells in the Quaternary aquifers are characterised by a calcium-bicarbonate major ion chemistry, with 65 samples from 25 wells and springs giving a median EC of 429 µS/cm (Jekatierynczuk-Rudczyk 2020). Thus, as with the Irish examples, these springs are not highly mineralised. In terms of potability, high iron concentrations were highlighted as a problem (elevated iron values are also a common feature of Irish groundwaters, including holy well samples).

The Austrian study included sampling of 21 holy springs in the east of the country (Kirschner et al. 2012; no details of locations or local geology are given). The majority of the springs did not meet the national drinking water standards, with coliform bacteria discovered in 76% of samples and nitrate values in excess of 50 mg NO3/L in 22% of samples. The Irish study did not include microbiological samples; nevertheless, in view of the nitrate results, it is considered likely that coliform bacteria could be present in many well samples.

In the Tigray region of Ethiopia, holy springs occur along a stream in an area of Neoproterozoic stratigraphy, which includes metavolcanics, metasediments and granites. There is gold mineralisation within sulphide deposits and the spring waters in this area are sulphur-rich (sulphate in the range 400–450 mg/L). As well as the high sulphate, other parameters outside national drinking water standards include low pH, high total dissolved solids and high iron content (Berhe et al. 2023).

Reputed cures and health benefits

Sacred springs and wells are linked to beliefs in the powers of healing in many cultures. Rituals may include drinking the water, rubbing the affected part of the body with a rag dipped in the holy water (which is then attached to a sacred tree, with the hope that the ailment disappears as the rag rots away) or bathing in the spring. In a study of holy wells and water cults in Britain and Ireland, Bord and Bord (1985) mentioned 75 different ailments for which cures were reported at holy wells. The most common reputed cure was for eye ailments, but other common cures were for warts, lameness, toothache, leprosy and infertility. Other writers have also commented on reputed health cures, including the frequency of cures for sore eyes (Varner 2009; Oestigaard 2013). In the Tigray example in Ethiopia, people drink the water for its purgative effects and perceived treatment of gastrointestinal ailments (Berhe et al. 2023). However, it is also important to stress that the spiritual dimension (including the belief of the pilgrim in a cure) and the attractive settings of many holy wells (sometimes referred to as therapeutic landscapes) are probably important elements in their healing reputations (Foley 2010).

Reputed cures were linked to 57% of the 215 wells in Ireland surveyed by Misstear (2023). Again, eye cures were the most common (reported in 27% of wells surveyed), followed by general or unspecified cures (14%), rheumatic and arthritic pains (11%) and toothache (8%). The healing reputations did not appear to be related to lithology: “eye wells”, for example, were found in all the main lithological groupings, and in rough proportion to the number of wells sampled in each group.

In relation to the number of wells sampled for water quality analysis that have reputations for cures (96 out of 167), statistical analyses (using Mann–Whitney U tests for nonparametric data) did not find any links between reported cures and the water chemistry in the majority of cases. However, the major ions sodium and chloride were significantly different statistically between “eye wells” and other wells, the median concentrations of both ions being higher in the samples from the eye wells. This finding is interesting, as bathing affected eyes in water enriched in sodium chloride is considered to be a beneficial modern treatment for eye irritation, albeit the salt concentrations were lower (14.3 mg/L sodium and 27.0 mg/L chloride in eye wells) than those in a common eye wash solution. The survey data also showed that eye wells are more common near the coast than the other wells, so elevated sodium and chloride concentrations would be expected.

International studies have shown that consuming groundwater can have nutritional benefits, although the majority of vital minerals are consumed via food (World Health Organization 2005; Hoque and Butler 2020). In the Irish research it was shown that up to 31, 14 and 8% of the recommended daily intake of calcium, magnesium and iron, respectively, could be obtained by drinking 2 L/day of water enriched in these ions (based on 95 percentile concentration values). Whilst some evidence of people drinking the water was found for ~27% of the wells surveyed, at the majority of sites the water consumption would be expected to be small, taken mainly as part of a ritual. These calculations of potential nutrient intakes, therefore, are more applicable to domestic supply wells than holy wells or springs. It is important to add, however, that, at least in Ireland, using a holy well for domestic purposes is often considered to bring bad luck. Indeed, according to folklore, a well may move position if it is ‘offended’, for example, by being used for washing clothes (Misstear 2023).

Discussion and conclusions

Sacred wells and springs have been significant features of many cultures and religions for centuries and, in some cases, millennia, and they need to be protected for future generations. It is evident that the water quality in many of these wells and springs may not always achieve potable standards. There is a need to increase awareness among the visitors to such wells about the potential risks of drinking from an untreated water source located in an area with potential pollution sources such as agricultural activities, waste disposal or industry. It is interesting to note that in the Austrian study cited previously, where many of the holy springs were found to be contaminated by faecal bacteria or nitrate, the authors observed parents ‘trying to convince their children of the high quality of the water’ (Kirschner et al. 2012).

The Irish study indicated that many of the holy wells are shallow springs and seeps in areas mapped as having extreme or high groundwater vulnerability. Although there were very few examples of water quality nitrate levels exceeding the drinking water standard, the concentrations in half of the wells were above background levels and, hence, suggestive of some anthropogenic impact. Bacteriological quality was not determined but, based on studies of private water supply wells (Hynds et al. 2012), it is likely that some of the holy wells are impacted, especially after heavy rainfall and also at times of the year when fertilisers are being applied to the land. There are some instances where the relevant local authority has placed signs at wells indicating that the water is not potable or that it is untreated, but such signs are rare.

Increasing the awareness of possible water quality issues amongst visitors to sacred wells and springs needs to be carried out with great sensitivity. These are, after all, sacred to many pilgrims, and drinking the water may be a key part of the religious ritual at a well. By publishing a book on the hydrogeology of holy wells, with its many text boxes explaining basic groundwater and water quality concepts for the general reader, it is hoped to contribute in a small way to this awareness-raising, whilst also respecting the values and beliefs of the pilgrims who visit and preserve our sacred well heritage.