This page has answers to frequently asked questions on the 'Microbiological water quality guidelines for marine and freshwater recreational areas'. The guidelines provide information to help councils and other agencies inform their communities of the risks related to swimming at bathing beaches.
Frequently asked questions
The term 'recreational water' describes any body of water (still or flowing) that people come into contact with while undertaking recreational activities (bathing, water sports, domestic shellfish collection etc).
Some regional councils identify water bodies of key recreational importance in their regional plans. For the purposes of applying the guidelines, a pragmatic approach to the designation of contact recreation areas should be adopted on a region by region basis. This would involve consultation between appropriate agencies and would be based upon factors such as beach access and popularity.
The guidelines cover the methods for monitoring and reporting on the public health risk associated with microbiological contamination in recreational waters (Refer Introduction section pp2).
The guidelines do not cover cyanobacteria or the public health risk associated with other effectors (eg chemical pollution, marine biotoxins) in a recreational context, or any risk associated with broader environmental values (ie the natural or resource value of the waters and aquatic species and habitats that they support).
The Microbiological Water Quality Guideline should be applied as the default and authoritative guideline for designated recreational waters as it places the objectives and methods of broader audience guidelines within a New Zealand context. There are however important conditions of guideline use that should be considered and these are summarised in sections D6 and E6.
Further information: Guidelines and documents relating to water quality and management for values other than recreational use, such as the ANZECC Water Quality Guidelines, can be found on the Ministry for the Environment website.
Guidance on a range of other hazards to the recreational use of water additional to those of a microbiological nature notcovered by specific NZ guidance can also be found in the World Health Organisations (WHO) guidelines for safe recreational waters.
International epidemiological studies have shown that E. coli and enterococci are more specific indicators of human health risk from recreational contact with fresh water and saline water than faecal coliforms.
E. coli and enterococci are members of the two bacteria groups, coliforms and faecal streptococci, respectively, and are used as indicators of possible sewage contamination because they are commonly found in human and animal faeces. Although they are generally not harmful themselves, they indicate the possible presence of pathogenic (disease-causing) bacteria, viruses, and protozoans that also live in human and animal digestive systems. Therefore, their presence in water bodies suggests that pathogenic microorganisms might also be present and that swimming and eating shellfish might be a health risk.
E. coli is relatively straightforward and inexpensive to measure. It can survive for up to four to six weeks in freshwater and is a definite indication of recent faecal contamination. While it is not possible to know whether E. coli are of human, animal or avian origin, all of these species can act as carriers of micro-organisms that can cause human disease. The chances of E.coli multiplying in water are very small, except under some specific tropical and sub-tropical conditions, so the number detected can be interpreted quantitatively.
Enterococci are distinguished by their ability to survive in salt water, and in this respect they more closely mimic many pathogens than do other indicators. Enterococci are typically more human-specific than the larger faecal streptococcus group.
Faecal coliforms are a subset of the coliform group. Although faecal coliforms are predominantly found in the intestinal tract of humans and other warm-blooded animals, they constitute a mixed group of organisms and some of the bacteria in this group can be derived from other environmental sources. They may also multiply in water on occasions to give a false impression of faecal contamination.
An example of the advantage of using E. coli as an indicator of human health risk is illustrated by the following case: a mismatch between faecal coliform (high) and E.Coli (low) results occured in March 2004 when a catchment on the North Shore (Auckland), upstream of a sampling point, was loaded with rotting vegetation. It is likely that in this case, certain strains of coliforms (Klebsiella, Enterobacter and Citrobacter) which are derived from vegetative sources were able to grow under the conditions defined for thermotolerant coliforms (faecal coliforms). Hence, total faecal coliform count was very high, but the actual pathogenic disease risk, as indicated more specifically by the E.coli count, was below guideline levels. It should be noted, in the context of this example, that regrowth of E.Coli can be associated with rotting vegetation at elevated temperatures. However, E.Coli must be present initially for regrowth to occur.
Further information: See Appendix 2 of the Microbiological Water Quality Guidelines for background information on the choice of indicators and advantages of using them. Also see FAQ 4 for information on quantifying the relationship between faecal coliforms and E.coli and enterococci.
This requires establishing a numerical relationship between the faecal coliform and E. coli and enterococci indicators.
If dual sampling has not been undertaken in the past, the USEPA ratios of 35 enterococci per 200 faecal coliforms (for seawater) or 126 E. coli per 200 faecal coliforms (for freshwater) could be applied. This approach would only be indicative but may be useful for management purposes and in assisting to identify high risk beaches.
If the intention is to define a MAC category on the basis of historical faecal coliform data, then a period of dual sampling (faecal coliform and E.Coli or enterococci) is needed to produce a site specific and statistically robust relationship for adjusting the historical data. An appropriate period would be two concurrent bathing seasons with intervening sampling if continuous sampling is routinely performed.
Further information: See Note H(v) of the Microbiological Water Quality Guidelines.
Concentrations of E.Coli and enterococci can be related to guideline levels to provide an indication of human health risk (in the form of likely numbers of illnesses per number of recreational events)
Defining the actual risk to public health indicated by a particular count of E.Coli or enterococci is not possible. This is primarily because these micro-organisms are indicators of the pathogenicity of water and not direct measures of disease causing organisms. The human response to pathogen concentrations and exposure varies from person to person and the relationship between risk and recreational events (eg swimmer numbers) is not necessarily a linear one. Hence the adoption of guidelines which define "acceptable" health risk limits is based upon international and New Zealand epidemiological studies of indicator:pathogen relationships and average human responses
Further information: See Appendix 2 of the Microbiological Water Quality Guidelines for detail on study results and interpreting human health risk.
For the purposes of local health advice and warnings, it is important to communicate to the public:
- beach grades
- exceedances of the Action level
Beaches grades are considered the most effective way of providing the public with sufficient information about the general state of a beach for them to make an informed decision about the risk of recreational contact.
Exceedances of Action levels need to be communicated promptly and effectively so that the public are aware as soon as possible of the direct health risk the water poses.
When communicating health risk you should relate single sample results to the guideline limits of acceptance and use qualifiers to recognise the uncertainties in statements being made. For example, "... if alert and action levels at a beach are exceeded the potential risk of illness associated with a recreational event is higher than 2% (19 per 1000)". This provides the audience with an indication of risk that can be related to, say, swimmer numbers. Examples of ways to effectively deter the public from using a body of water include beach signage, newspaper articles, web-based reporting and radio announcements. Remember it is equally important to effectively communicate to the public that a beach is safe to use following an event.
The most useful way to report on recreational water bodies is to provide beach grades and an assessment of the "suitability for use"
On a national level, the Ministry for the Environment propose to report data collected from the implementation of the guidelines in the following way:
- the percentage of monitored beaches in each beach grade, and
- the percentage of the season beaches or coastal areas are suitable for bathing or shell fish gathering.
Note that the threshold level used to determine the percentage time in compliance (for the second indicator) is the "Action Level" exceedance of 280 enterococci per 100ml.
The actual format and medium of national reporting has yet to be confirmed but there will be a process for public and practitioner feedback on the effectiveness of that reporting.
Further information: Some councils are currently presenting the results of recreational beach monitoring online. See the following web pages for some examples of this reporting:
Swimming water quality [Environment Canterbury Regional Council website] - A great example of how a council reports and communicates beach grades.
Auckland Council Safeswim water quality monitoring programme [Auckland Council website]
The following councils are reporting weekly data in a variety of useful formats:
8. In some recreational areas there is significant mixing of freshwater and saline water. What is the most effective way of implementing guideline monitoring in these areas? (includes practitioners experiences and recommendations)
In areas where the extent of freshwater/saline water mixing is not well understood, then multiple indicator monitoring may be appropriate to fully characterise the public health risk.
It is recognised that the application of the guidelines in recreational waters where there is considerable mixing of saline and freshwater (eg where a stream discharges to a coastal beach) will sometimes be problematic, as the indicator relationships can change and/or different indicators need to be considered. This aspect of the guidelines has been the subject of some debate and the following section provides comments, ideas and critiques from practitioners which may be helpful to others.
Dr Adrian Meredith - Water Quality Scientist, Environment Canterbury
"... my advice is that in any areas such as estuaries and beaches with stream mouths, or where there are certain discharge types, or where there is concern or confusion over sources, then it is strategically best to be monitoring for both indicators (E coli and enterococci). When shellfish gathering is also an issue, then quite simply that means three indicators (and we do have beaches in Canterbury where we have to do that). My message - accept that situation (and additional cost) as a feature of the current state of science and the guidelines.
Brett Stansfield - Environmental Scientist-Water Quality, Hawkes Bay Regional Council
"... When it comes to bathing guidelines we pretty much do what is recommended in the Microbiological Water Quality Guidelines. However if this programme (or any other programme) identifies poor bacteriological water quality, in freshwater we will monitor for 3 indicators, faecal coliforms, enterococci and E.coli. Why?
- Faecal coliforms - because like most regional councils we have a long historical record of faecal coliforms in our region from which comparisons can be made.
- E. coli - to determine how many of the faecal coliform group are E.coli
- Enterococci - Because E.coli and Enterococci have different survival rates in water we use the Ent/E.coli ratio to see if any areas within the catchment point towards more recent or continuous sources of contamination
- If we're really worried about a waterbody's water quality and it is in a residential area we will follow up with faecal sterol analysis and a test for whitening agents to determine whether the contamination is of human or animal origin."
Trevor James - Environmental Monitoring Officer, West Coast Regional Council
"... We sample for all 3 parameters (enterococci, Faecal coliforms & E.coli) in brackish waters and along a fresh-saline continuum if a sanitary survey is required. Faecal coliforms have been found to be a very good indicator of discharges from waste stabilistation/oxidation ponds (Lester Sinton, ESR has written a paper on this) - this includes discharges to the marine environment. We have got most of our marine outfalls from waste stabilistation/oxidation ponds to monitor this parameter for marine waters."
The Sanitary Inspection Category (SIC) is based upon the hazard assessment approach taken in the Annapolis Protocol, a microbiological monitoring scheme developed by the World Health Organisation (WHO 1999).
The Annapolis Protocol framework has been adapted for New Zealand application in accordance with recommendations by expert scientific and practitioner working groups established by MfE for the purpose and field trials.
The rationale behind defining the Sanitary Inspection Categories (SIC) is shown in Tables H2 and H3 of the guidelines. The SIC is an assessment of sources of potential faecal contamination within a catchment and the risk they pose to a recreational site.
The guidelines recommend reporting a beach "unsuitable for recreational use" after the Action Level is exceeded by two consecutive samples for marine water and one sample for freshwater.
Two results are required in marine water because contamination events in marine water are more likely to be episodic and fast changing, than in freshwater where there is less likelihood of rapid dilution or flushing. The second sample in marine waters is taken to confirm the first and that contamination is still present. However, if contamination is obvious and likely to be ongoing it is not necessary to wait for results from samples (1st or 2nd) before issuing a health warning (see Note H(xvii)). Remember, the main objective of the guidelines is to protect public health. If you know from experience that the beach is going to be contaminated (e.g. following heavy rainfall or a wastewater spill) then the public should be notified as soon as practicable.
Further information: The recommended course of action to be taken once an exceedance result is obtained is summarised in Box 1 (Part II: Section D: Microbiological Guidelines for Marine Waters) and Box 2 (Part II: Section E: Microbiological Guidelines for Freshwaters) in the Microbiological Water Quality Guidelines.
Site specific investigation should be undertaken to quantify effects unless contamination events associated with the risk factor can be accurately predicted and built into an effective communication strategy.
If you do not specifically investigate and measure the effect of each factor it may not be possible to determine the related impacts with any certainty. In such cases it is appropriate to make an interim decision based upon expert opinion and site specific knowledge, however, as noted on page H18 of the guidelines, "... a more detailed investigation may be required to establish the relative importance of the effect". The onus must be on the agency implementing the guidelines to ultimately prove the effect of an identified factor so that confidence can be had in the beach grade.
In some instances a factor deemed "present" may only have an effect on a very intermittent basis. Using the example of a sewage overflow, if you know the environmental conditions (eg heavy rainfall) that lead to an overflow and pathogen exceedances in nearby recreational waters, and you are able to effectively warn the public, then you can discount this factor and its risk contribution from the beach grade. You may end up with a grade of "Good - except for 2 days after heavy rainfall". If you are unable to adequately predict overflow events then you cannot discount it as a factor from the beach grading.
Another example is of a stream with high E. coli levels that discharges to a beach. If you can show (by dye testing for example) that the mixing zone of the stream does not overlap with designated recreational beach waters then you may be able to discount it as a risk factor from the beach grade. Of course, investigation of the mixing zone would need to be carried out during a range of conditions, to account for variations in tide and current, wind, beach profile and stream flow, and on a sufficient number of occasions to validate the results.
Where multiple sources exist the practitioner must choose the most important to rank as the "primary effect".
The guidelines are deliberately conservative (a common guideline approach) and categorise a beach according to its highest ranked risk source. The risk ranking in the guidelines is set according to the faecal load of the effluent source. Guidance on deciding which is the most important source of risk is given in Note(iii), page H5. It is important to note that the ranking of effects cannot be done in the absence of knowledge specific to those effects. In addition to the collection of measurement data, anecdotal observations from local council and health workers, and residents may help to identify the relative significance of risk sources.
It has been observed by some practitioners that a beach with only one significant risk source (eg polluted stream discharge) may get the same SIC grading as a beach that has multiple risk sources (eg polluted stream and stormwater outlets). However, it is not essential for the differentiation of beaches, with respect to likely water quality impacts of single and multiple risk sources, to be made in the SIC assessment. If a marked difference in water quality exists then the MAC should serve to differentiate these beaches in the final grading.
It should be assumed that some sewage ingress is taking place when ranking the risk posed by a stormwater discharge
Unless you can discount faecal loading by dedicated monitoring of the outfall under a range of conditions then a conservative approach should be adopted to ranking the risk. It is important to bear in mind that even if urban stormwater networks have been installed as protected conduits they can still receive significant faecal loading (eg bird, cat & dog droppings and unauthorised and/or illegal/accidental cross connections).
Further information: Refer to FAQ 11 - effect of risk factors
BatheWatch is a software package that helps practitioners use the guidelines and derive beach grades.
The software guides users through the process required to grade marine freshwater and recreational areas as very good, good, fair, poor, or very poor. The software is available to download from the Ministry for the Environments website. The software is very easy to use and comes with a comprehensive users guide for step by step instruction.
A recent survey of BatheWatch users, found that the majority of users found the software useful to determine their beach grades (This survey document will be available on the MfE website later in 2004). Opportunities for improving the software have been identified by users and MfE are currently working on an upgrade.
15. What are the sample requirements to achieve a full SFRG from the BatheWatch software? (as opposed to an interim grading)
100 samples taken in 5 consecutive years
The BatheWatch software requires a minimum of 20 samples to calculate a MAC and a minimum of 100 samples in five consecutive years to generate a full SFRG. In generating the SFRG it does not require 20 samples in each year (eg you could have 20, 15, 25, 10, 30). However, if you include a gap year (ie year without any monitoring results) you will only be able to achieve an interim grading.
A most important issue in assessing the microbial water quality is that of collecting sufficient numbers of samples so as to make an appropriate estimation of the likely densities to which recreational water users are exposed. Twenty samples is the optimum for calculating the 95th percentile (below which there is decreasing confidence in the result and above which the returns diminish very quickly).
The number of results available can be increased significantly - and with no additional cost - by pooling data from multiple years. This practice is justified unless there is reason to believe that local (pollution) conditions have changed, causing the results to deviate from established behaviour. For practical purposes, it is suggested that data on at least 100 samples from a 5-year period and a rolling 5-year data set be used for microbial water quality assessment purposes. In many situations, a much shorter period will be required, where, for example, more extensive sampling is undertaken. As well, fewer samples may be required - for instance, where the water quality is very poor.
16. Should I exclude targeted monitoring data (eg data collected when assessing the risk of a sewage outfall) from the overall MAC and beach grading dataset?
Data that is collected during an intensive measurement period (eg daily for 3 weeks) may skew a dataset that otherwise comprises weekly measurements over a bathing season, particularly if your beach does not have a long history of sampling. Including "datasets within datasets" may over-represent the influences of certain environmental factors (eg climatic and flow regimes) that are averaged out in the more regular frequency monitoring results. However, samples from these intensive monitoring periods should be included when they coincide with scheduled "surveillance" monitoring (ie one sample should be representative of a consistent period of time).
The method recommended to calculate the 95th percentile is the Hazen method.
A Hazen percentile calculator is packaged up into the BatheWatch software and will automatically calculate the 95th percentile of entered data for you. If you want to use this calculator independently of Bathewatch, or if you are interested in how the 95th percentile is calculated, follow the link below to an excel spreadsheet that contains a Hazen percentile calculator, guidance on how to use it, and comparisons with other percentile calculators.
Further information: Hazen Percentile Calculator [Excel spreadsheet 226 KB]
If you have any queries about the Hazen Percentile Calculator please send us an email, firstname.lastname@example.org.
Concentrate your efforts on beaches that are consistently heavily used and have a history of variable water quality.
The guidelines are intended to be a practical tool for effective public health warning. As such, a balance needs to be struck between achieving representative risk assessment and monitoring and being able to provide sufficient resources to maintain a monitoring programme long term. It is acknowledged that at some locations the monitoring requirements may be substantial, at least to begin with, because of the complexity of risk sources or the need to sample for multiple indicators (eg FAQ 8). However, in general terms there are some basic actions that can be taken to economise on the overall monitoring effort:
- Do not monitor at locations where contact recreational use is rare. Concentrate your efforts on beaches that are heavily used for the whole of the summer season.
- Concentrate on "Good", "Fair" and "Poor" beaches. Where beaches have been found to be consistently "Very Good" it may be possible to stop monitoring regularly and simply communicate a strategy to the public so that they know what conditions may lead to a deterioration of the water quality.
- Where the effects of the influencing factors are highly predictable (timing and duration) a management and communication strategy rather than a sampling programme may be sufficient. However, a comprehensive beach water quality monitoring dataset combined with specific investigations and measurements of contributing factors would be required before factors can be accurately predicted; ie the SFRG should be established at a beach (see FAQ 15) before monitoring is reduced. After this point, annual assessment should be undertaken to identify any change in the SIC that could alter the grading.
- Share monitoring responsibilities between agencies, especially where there are large distances to be covered to collect samples.