Sample and questionnaire design

The CV questionnaire was developed and pre-tested over a 4 week time period in March and April 2006. Eight trained interviewers were used to pre-test the questionnaire through 152 face-to-face interviews with general public. Different groundwater experts from governmental and non-governmental expert institutions were consulted for the information statements used in the questionnaire. The final version of the CV questionnaire was sent by mail to 2,800 randomly selected households in Zeeland (Scheldt basin) on 19 May 2006⁶. The response rate for Zeeland is 18 percent (n=520). Two respondents appeared to be below 18 years old and were excluded from the database, resulting in a total number of observations of 518.

The questionnaire follows Dillman’s (1978) total design method and consists of the following six parts:

• General introductory questions about respondents’ drinking water use, sources of drinking water, and knowledge about current prices for both tap and bottled water.

• The second part consists of a series of questions about respondent perception of current water quality in general (surface and groundwater) and groundwater more particularly, respondent familiarity with groundwater and groundwater quality in the basin, and the importance attached to groundwater protection.

• In the third part, groundwater quality problems are introduced in general (see Box 1) and respondents are asked how familiar they are with the information provided, how important it is for them personally to improve groundwater quality and how familiar they are with groundwater polluting substances and whether they are able to mention some of these polluting substances.

6 The provincial government is the groundwater authority in the Netherlands, responsible for all aspects of groundwater management.

Groundwater is an important source for drinking water. About two thirds of all tap water used by households in the Netherlands stems from groundwater. The remainder is pumped up from surface water (lakes and rivers).

Different land use forms such as urban areas, industrial sites, agriculture and landfills exert pressure on groundwater. Poor groundwater quality results in high purification costs of your tap water and also has a negative effect on the quality of connected surface water in lakes, rivers and ditches and on groundwater dependent nature.

Although action has been undertaken in the past years to improve groundwater quality, much groundwater in the Netherlands is still of poor quality. In many places one or more polluting substances can be found resulting in poor groundwater quality. This is illustrated for example in the map on the next page. The map shows the current concentration levels of nitrate in groundwater. The areas in red represent the most vulnerable areas and where most groundwater pumping stations are located for drinking water, also for the greener parts in the north-west of the country. If no additional action is undertaken, the quality of all groundwater bodies will deteriorate in the future.

Box 1: Introduction groundwater quality problems in general

• The fourth part of the questionnaire relates to the WTP question. A second text box introducing four different groundwater quality classes (in colour corresponding with the colours in the map introduced in the first text box) explains that European cooperation aims to achieve good or very good groundwater quality in the next 10 years. Per groundwater quality class a short explanation is provided.

It is this translation of groundwater quality threshold values into understandable and meaningful quality classes to a larger lay public that took a lot of time and effort during the pre-test phase of the questionnaire. Presenting lay public with different concentration levels of groundwater quality does not work. Also the use of terms like

‘good’ or ‘very good’ requires further explanation and clarification in order to be able to produce meaningful answers to the questions related to public preferences for groundwater quality levels. A delicate balancing act is needed here to assess how much and which type of information is required to make respondents understand the meaning of the quality levels in a relatively short period of time, without overloading respondents with information.

Groundwater quality class Corresponding norm for example for nitrate Very good Natural situation 0-25 mg nitrate per litre

Good Drinking water quality 25-50 mg nitrate per litre Moderate Irrigation water quality 50-100 mg nitrate per litre

Poor Not useable >100 mg nitrate per litre

Natural background quality: no polluting substances are found in groundwater that are not naturally there already. Under natural conditions certain substances like nitrate are found in groundwater in small quantities only.

Drinking water quality: groundwater is clean enough to drink without any treatment and without any risk for public health.

Irrigation water quality: groundwater is clean enough to be used to irrigate your garden or flush your toilet, but cannot be drunk without treatment first.

Not useable: groundwater quality is too poor to be used for anything without treatment first, including irrigating your garden.

Box 2: Introduction groundwater quality classes

After the introduction of groundwater quality problems and possible groundwater quality classes, respondents are informed that improving groundwater quality is costly: the cleaner the water, the higher the associated clean-up costs. Taking this into account, respondents are asked which groundwater quality level they prefer and how difficult it is for them to assess what the various groundwater quality classes mean and imply for them personally.

In a small third text box examples of possible measures are presented and respondents are reminded of the fact that taking additional action comes at a cost, and that when applying the polluter pays principle they too contribute to the deterioration of groundwater quality.

In order to improve groundwater quality in the next years, additional action will have to be taken to reduce current pollution levels from households, agriculture and industry and prevent future pollution. Examples of such measures include:

• additional household wastewater treatment

• less fertilizer use on agricultural land

• clean-up of polluted industrial sites

These measures come at a cost. Agriculture and industry contribute according to the ‘polluter pays principle’.

Box 3: Introduction possible groundwater protection measures

After this, respondents are asked whether they are willing to pay in principle to reach their most preferred groundwater quality level as indicated in the previous question in their own region. If not, they are asked why not and directed to the fifth part of the questionnaire. If they are willing to pay, they are first asked for which area they are willing to pay and for what reason, using a continuous use-nonuse scale. Then they are asked to indicate on a payment card, displaying 30 values ranging from €0 to €300 (going from 0 to 300 from left to right), how much they are willing to pay maximum for the next 10 years in general income taxation to reach their most preferred

groundwater quality level in the year 2015 in the area for which they are willing to pay. The WTP question is formulated as follows:

‘Please indicate on the card below how much extra taxation you would be willing to pay at most on behalf of your entire household for the next 10 years to reach your most preferred groundwater quality level in the year 2015’

The payment card includes the options:

- I don’t know

- More than €300, namely € ……..

- Other amount, namely €……..

It is pointed out explicitly that the money amount respondents are willing to pay will be used exclusively to finance the costs of the necessary additional measures to improve groundwater quality.

After selecting and crossing a money amount respondents are asked why they are willing to pay this specific amount and how certain they are that they will actually pay this amount. If they are not 100% certain, they are asked why not and how much they are willing to pay at most with 99 percent certainty to reach their most preferred groundwater quality level.

Those respondents who prefer irrigation or drinking water quality are also asked if they are willing to pay in principle for reaching a natural situation and if so, how much extra they are willing to pay to reach a situation with natural background levels, using the same payment card again. It is made explicitly clear that this money amount is over and above the amount they stated for their most preferred groundwater quality level.

• The fifth part of the questionnaire consists of standard questions related to respondents’ demographic and socio-economic characteristics.

• The sixth and final part of the questionnaire focuses on respondent opinion and perception of the questionnaire self.