Safer drinking water

Identifying and managing strategic drinking water resources. “Water is not a commercial product like any other but, rather, a legacy which must be protected, defended and treated as such”. This is written into the EU’s framework water directive, which aims to ensure access to water of sufficient quality for the sustainable, balanced and equitable use of water. Water is also our most important foodstuff and, for this reason, must be handled in a safe manner, from the source to the consumer. In recent years, climate changes and major outbreaks of water-borne diseases in Sweden have once again brought these requirements to the fore.

Tyréns is currently running a development project comprising several subprojects, which are described below, all of which aim to increase our knowledge in order to secure a safer supply of drinking water.

Identifying and managing strategic drinking water resources
By developing a method in which strategic drinking water resources are systematically identified and managed in a transparent way, the chances are increased that they will be available in the future despite climate changes and competing interests.

A more general method, which is based on multi-criteria analysis, has been developed. This can also be used as an aid to decision making in other questions concerning the drinking water supply. It is important for the method be transparent because the conditions and valuation criteria may change over time and may be affected by various events such as, for example, outbreaks of water-borne disease. In such a case, it will be possible to work back through the chain and adjust the criteria or ranking without needing to start again from the beginning.

The method that has been developed in the project has been applied to a number of case studies concerning different types of issue. These include providing data for analyses of a municipal water supply plan as well as providing data for choosing a long-term sustainable water and wastewater supply in a transformation area. It has also been used to provide support for analysis and comparisons between different water resources or water intakes as data for strategic choices, including the analysis of different alternatives and strategies for backup water supply in Stockholm County. In connection with the applications, the method has been tested from different angles and contexts, which has resulted in its subsequent further development.

GIS support for prioritising parasite sources – evaluation of proliferation models
The Cryptosporidium and Giardia parasites have caused expensive outbreaks of water-borne diseases in Scandinavia in recent years. Geographical Information Systems (GIS) can be helpful in localising the sources of proliferation in the run-off area and, combined with hydrological modelling, constitute a powerful tool for analysing the health risks of raw water.

The aim of this project was to evaluate the usefulness of the Soil and Water Assessment Tool (SWAT) for analysing the origin and proliferation of E. coli as well as other species of the Cryptosporidium parasite in surface water intakes. An interdisciplinary project group and a reference group with the authorities concerned has assisted in assuring the quality of the model design.

Three SWAT models were set up, two within the run-off area for the Göta Älv river (the Slumpån river and upstream of Trollhättan’s raw water intake) and one in Lake Mälaren’s run-off area (upstream of Stäket). The sources of proliferation included municipal wastewater (emissions from sewage treatment plants and overflow points), private wastewater, muck spreading as well as grazing stock.
In order to give a representative picture of probable and relevant conditions, modelling was performed for various scenarios. Five base scenarios (S0A-S0E) were chosen to describe probable situations regarding the spread of faecal material and various levels (prevalence) of Cryptosporidium infection in humans and animals.

Seven action scenarios (S1-S7) were analysed, where the effect of the measures taken in the run-off areas were presented as a log-reduction compared to the base scenario, S0D. The best fit to the modelled and measured levels of E. coli were in the Trollhättan model area. For this area, an infection risk analysis (MRA) was performed.

The run-off areas with relatively detailed information on point sources and diffuse sources (Slumpån river) are better suited for analysis with the SWAT tool compared to the large run-off areas where there is scanty information about the point sources (Lake Mälaren) or where the inflow to the model area largely controls the microbiological levels at the outflow node (Trollhättan). SWAT could possibly be used for calculating the proliferation of other pathogens, for example norovirus.

Ground water that is safe for health in a changed climate: Microbial risk analysis
The influence of wastewater is a common cause of water-borne infections in the production of drinking water based on ground water. For municipal ground water intakes, the awareness and opportunities for protection are presumably greater than is the case for private drinking water wells, but even in these facilities, water-borne infections occur. For municipal drinking water treatment plants taking their supply from surface water, microbial risk analysis (MRA) has been in use for several years as a tool to estimate the infection risk for a specific system, where the raw water quality and separation in preparatory stages during normal operation and during impaired function affect the risk. For ground water treatment plants, the industry has lacked an analysis tool for quantifying the microbiological risks, this includes for assessing the barrier effect in saturated and unsaturated zones.

In this project, a MRA tool has been developed and implemented to estimate infection risks for municipal ground water treatment plants and for private drinking water wells. The project, which was performed jointly with drinking water researchers at Chalmers, included:

  • Identifying ground water intakes subject to microbiological risks, describing sources of proliferation and microbiological barriers;
  • Based on literature studies, selecting methods for estimating the reduction of bacteria, viruses and parasites in saturated and unsaturated zones;
  • Establishing estimation models in the Analytica® software, where this information is used for the risk analysis of municipal ground water treatment plants;
  • Implementing the MRA tool in three case studies at municipal ground water intakes;

While groundwater intakes with natural infiltration may be exposed to pathogens from small drains, leaking sewers and muck spreading, basin infiltration means that large volumes of the surface water are infiltrated, with a consequently potentially large risk for a small unsaturated zone and short transport times. Viruses from humans, for example the norovirus, are the category of pathogens with the best chances of penetrating soil strata; however, the transport, and thus the risk, is controlled by both natural and operational factors.

An MRA tool for ground water treatment plants has been developed in Analytica®, where the results from field tests are implemented in the calculation modules for bacteria, viruses and parasites in unsaturated and saturated zones. A calculation module has been set up for modelling the transport of viruses in saturated zones. The MRA tool builds on the existing model for surface water treatment plants and, thus, can be easily extended with additional preparation steps, such as UV light. The tool has been evaluated in several case studies; two in the ground water intakes at Forslunda in Umeå Municipality and one in Magra, Alingsås Municipality. The results from the analyses have been presented and discussed with each municipality.

Method for formulating water protection regulations
The formulation of water protection for municipal sources of water is a hard and extensive process. The study aims at developing a method to streamline the work with formulating regulations as well as to raise the quality and the legal security. This has included developing the coupling between the regulations and a risk analysis.
The regulations drawn up must be legally sustainable. Regulations are frequently questioned. In the study, the possibility of considering case law as early as the formulation of the regulations was investigated. It must be possible to justify the restriction levels selected. Today, there are no recommendations on how this process should be pursued and documented. In many cases, the available recommendations are contradictory and difficult to apply in practise. The conclusion is that they need to be revised and developed, this includes taking into consideration other legislation.
In the study, case law and guideline judgements, where water protection regulations were examined, were inventoried. The bodies from which such decisions and judgements were taken include the Government, the Land and Environmental Court and the Supreme Administrative Court. A comparison was then made with the Swedish Environmental Protection Agency’s general recommendations.
In the project, a method was developed for making risk assessments and how this should lead to a risk level. A specification of what constitutes risk in an activity. For example, pesticides can involve a risk during transport, storage and spreading. The different risks associated with the example of pesticides may need to be described and regulated in different ways. The method will make possible structured work including risk assessment.

Hydraulic conductivity
In the project, a method was identified for describing the conditions for ground water movements in a significantly easier way than is the case in conventional hydrogeological surveys.
In the “Slug-interference” method, wave movements in the ground water are used to determine the ground’s properties. A pressure wave is induced at one point and it is read off at several other points. The calculation program transforms the wave movements measured into hydrogeological parameters. A suitable program has been selected for this purpose and the method will be evaluated in trials and compared to conventional methods.

Client: Sven Tyréns Stiftelse