Waters Protection Act (WPA)
English is not an official language of the Swiss Confederation. This translation is provided for information purposes only and has no legal force.
Chapter 1 Maintaining the Quality of Waters
Section 1 Discharge, Introduction and Infiltration
Art. 6 Principle
1 It is prohibited to introduce into a body of water, either directly or indirectly any substances which may pollute it; the infiltration of such substances is also prohibited. 2 It is also prohibited to store or spread such substances outside a body of water if there is a genuine risk of water pollution.
Art. 7 Disposal of wastewater
1 Polluted wastewater must be treated. It may only be discharged or infiltrated into a body of water with the authorisation of the cantonal authority. 2 Non-polluted wastewater must be discharged by infiltration according to the instructions of the cantonal authority. If local conditions do not permit this, such non-polluted water may be discharged into surface waters; in this case retention measures must be taken if possible so as to ensure a steady discharge in the event of high inflow. The discharge of water that is not shown on a communal drainage plan approved by the canton requires the consent of the cantonal authority. 3 The cantons shall arrange the drawing up of communal and, if required, regional drainage plans.
Para. 2 — Amended by No I 3 of the FA of 21 Dec 2007 on the Abolition and Simplification of Licensing Procedures, in force since 1 June 2008 (AS 2008 2265; BBl 2007 315). Para. 3 — Inserted by No I of the FA of 20 June 1997, in force since 1 Nov. 1997 (AS 1997 2243; BBl 1996 IV 1217).
Art. 8
Repealed by Annex No 2 of the FA of 21 Dec. 1995, with effect from 1 July 1997 (AS 1997 1155; BBl 1993 II 1445).
Art. 9 Federal Council regulations on the discharge and infiltration of substances
1 The Federal Council shall specify the water quality requirements for surface and underground waters. 2 It shall enact regulations on: a. the discharge of wastewater into bodies of water; b. the infiltration of wastewater; c. substances which may according to the method of their use enter into water and which, by reason of their properties or the quantities used, risk polluting waters or impairing the operation of wastewater treatment plants. 3 An authorisation for plant protection products and biocidal products (pesticides) must be reviewed if: a. the limit value of 0.1 µg/l for pesticides or their degradation products is repeatedly and widely exceeded in waters used or intended for use for drinking water; or b. the ecotoxicological limit values for pesticides are repeatedly and widely exceeded in surface waters. 4 The new decision on authorisation must ensure compliance with the limit values. 5 If it is not possible to achieve compliance with the limit values by imposing conditions
Para. 3 let. b — Inserted by No I 2 of the FA of 19 March 2021 (Amendment of the Chemicals Act, the Waters Protection Act and the Agriculture Act), in force since 1 Feb. 2023 (AS 2022 263; 2023 2; BBl 2020 6523, 6785). Para. 4 — Inserted by No I 2 of the FA of 19 March 2021 (Amendment of the Chemicals Act, the Waters Protection Act and the Agriculture Act), in force since 1 Feb. 2023 (AS 2022 263; 2023 2; BBl 2020 6523, 6785). Para. 5 — Inserted by No I 2 of the FA of 19 March 2021 (Amendment of
Section 2 Treatment of Wastewater and Use of Farm
Art. 10 Public sewers and central wastewater treatment plants
1 The cantons shall be responsible for the construction of public sewers and central plants for the treatment of polluted wastewater: a. from building zones; b. from existing groups of buildings outside building zones for which the special procedures for the disposal of wastewater (Art. 13) provide insufficient protection for waters or are not economically viable. 1bis They shall ensure that these plants are operated economically. 2 In isolated or sparsely inhabited regions, polluted wastewater must be treated by systems other than central wastewater treatment plants provided that the protection of surface and underground waters is guaranteed. 3 If private sewers also serve the public interest, their status is equal to that of public sewers. 4 ...
Para. 1bis — Inserted by No I of the Federal Act of 20 June 1997, in force since 1 Nov. 1997 (AS 1997 2243; BBl 1996 IV 1217). Para. 4 — Repealed by No I of the FA of 20 June 1997, with effect from 1 Nov. 1997 (AS 1997 2243; BBl 1996 IV 1217).
Art. 11 Duty to connect to sewers and to accept polluted wastewater
1 Polluted wastewater which originates in an area served by public sewers shall be discharged into such sewers. 2 The areas served by public sewers shall include: a. building zones; b. other zones as soon as they are connected to the public sewers (Art. 10 para. 1, let. b); c. other zones where connection to the public sewers is expedient and reasonable. 3 The person responsible for the sewers is obliged to accept wastewater and convey it to the appropriate central wastewater treatment plant.
Art. 12 Special cases in areas covered by public sewers
1 Those responsible for wastewater which does not meet the requirements laid down for discharge into the drainage system must subject such wastewater to pre-treatment. Such pre-treatment shall be regulated by the cantons. 2 The cantonal authorities shall decide on the appropriate way to dispose of wastewater which is not suited for treatment by a central water treatment plant. 3 Non-polluted wastewater with permanent flow shall not be passed through a central wastewater treatment plant either directly or indirectly. The cantonal authorities may authorise exceptions to this rule. 4 In a farm comprising a substantial stock of cattle or pigs, domestic wastewater may be used agriculturally together with the liquid manure (Art. 14) provided that: a. residential or industrial buildings and their adjoining land are situated in an area classified as an agricultural zone or the communal authority is taking the necessary measures, particularly in the field of area planning, to classify the build
Art. 13 Special procedures for the disposal of wastewater
1 Outside areas covered by public sewers, wastewater shall be disposed of by state-of-the art methods. 2 The cantons shall ensure that water quality requirements are respected.
Art. 14 Animal husbandry farms
1 All animal husbandry farms must attempt to balance their use of manure. 2 Farm manure shall be used in agriculture and horticulture in an environmentally compatible way and according to the state-of-the-art. 3 The farm must have storage facilities with a capacity for at least three months. However, the cantonal authorities may require a higher storage capacity for establishments situated in mountain areas or in areas with unfavourable climatic or special crop growing conditions. Lower storage capacities may also be authorised for buildings which are occupied by livestock for only short periods of time. 4 A maximum of three livestock units of manure may be spread on 1 ha of agricultural land. If part of the farm manure is used outside the normal local farming area, the number of animals kept must be such that at least half the manure produced by the farm may be used on the agricultural land owned or leased. 5 Farms that provide manure must record each delivery in the information syste
Para. 4 — Amended by Annex No 6 of the FA of 22 March 2013, in force since 1 Jan. 2014 (AS 2013 3463 3863; BBl 2012 2075). Para. 5 — SR 910.1 Para. 5 — Amended by Annex No 6 of the FA of 22 March 2013, in force since 1 Jan. 2014 (AS 2013 3463 3863; BBl 2012 2075).
Art. 15 Construction and inspection of installations and equipment
1 The persons responsible for wastewater treatment plants, storage facilities and technical processing plants for farm manure and liquid digestate as well as of raw fodder silos shall ensure that these are used, serviced and maintained in an appropriate manner. The correct functioning of wastewater treatment plants and processing plants for farm manure must be checked at regular intervals. 2 The cantonal authorities shall ensure that such installations are inspected periodically.
Art. 15 — Amended by No I of the Federal Act of 24 March 2006, in force since 1 Jan. 2007 (AS 2006 4287; BBl 2005 937). Para. 1 — Amended by Annex No 6 of the FA of 22 March 2013, in force since 1 Jan. 2014 (AS 2013 3463 3863; BBl 2012 2075).
Art. 16 Federal Council regulations on wastewater treatment and the inspection of installations
The Federal Council shall lay down the requirements for: a. discharge into sewers; b. special releases from production processes; c. residues from wastewater treatment plants, their recovery and disposal; d. the inspection of installations and equipment; e. the use of wastewater issuing from the processing of farm manure.
Section 3 Technical Wastewater Requirements for th
Art. 17 Principle
Building permits for new buildings and building alterations shall be granted only if: a. in areas served by public sewers, polluted wastewater is discharged into the sewers (Art. 11 para. 1) or used for agricultural purposes (Art. 12 para. 4); b. outside areas served by public sewers, the appropriate disposal of polluted wastewater is ensured through special procedures (Art. 13 para 1); the cantonal water protection agency shall be consulted to this effect; c. there is a guarantee that wastewater which is unsuitable for treatment by a central wastewater treatment plant may be disposed of in an appropriate manner (Art. 12 para. 2).
Art. 18 Exceptions
1 In the case of small buildings and installations in an area served by public sewers but which for overriding reasons cannot be immediately connected to such sewers, a building permit may be granted where it is possible to provide the connection in the short term and that in the meantime the wastewater may be disposed of in another satisfactory manner. Before the authority grants a building permit in such circumstances, it shall consult with the cantonal water protection agency. 2 The Federal Council may define the exceptions in greater detail.
Section 4 Protection in terms of Area Planning
Art. 19 Water protection areas
1 The cantons shall divide their territory into water protection areas according to the risks of pollution to which surface and underground waters are subject. The Federal Council shall enact the required regulations. 2 In areas which are particularly vulnerable, the construction and conversion of buildings and installations as well as operations such as excavations, earthworks and similar works may take place only provided that a cantonal permit has been granted if they may pose a risk to the waters.
Para. 2 — Amended by No I of the FA of 24 March 2006, in force since 1 Jan. 2007 (AS 2006 4287; BBl 2005 937).
Art. 20 Groundwater protection zones
1 The cantons shall determine protection zones for groundwater wells and recharge installations serving the public interest; they shall lay down any limitations on property rights which may be required to this effect. 2 The persons responsible for groundwater wells must: a. carry out the surveys necessary to establish the boundaries of protection zones; b. acquire the necessary rights in rem; c. bear the cost, where applicable, of compensation paid in respect of limitations on property rights.
Art. 21 Groundwater protection areas
1 The cantons shall determine areas which are of importance for the future use and recharge of groundwater resources. In such areas, no buildings or installations may be constructed, and no works shall be carried out which might adversely affect any future installation built to use or replenish the groundwater. 2 The cantons may transfer responsibility for paying compensation in respect of limitations on property rights to persons subsequently responsible for groundwater wells and recharge installations.
Section 5 Handling Liquids which may pollute Water
Art. 22 General Requirements
1 The persons responsible for installations for handling liquids which may pollute water must ensure that the structures and equipment required for the protection of the waters are provided, regularly inspected and properly operated and maintained. Storage installations that require a permit (Art. 19 para. 2) must be inspected at least every ten years; depending on the risk of pollution to the waters, the Federal Council may stipulate inspection intervals for other installations. 2 Losses of liquid must be prevented at storage installations and transhipment areas and leaks of liquid shall be easily detected and retained. 3 Installations with liquids which may pollute water may only be constructed, modified, inspected, filled, maintained, emptied and decommissioned by persons who due to their training, equipment and experience guarantee compliance with the state of the art. 4 Any person who manufactures parts for installations must test whether these parts correspond to the state of the
Art. 22 — Amended by No I of the FA of 24 March 2006, in force since 1 Jan. 2007 (AS 2006 4287; BBl 2005 937).
Art. 23
Repealed by No I of the FA of 24 March 2006, with effect from 1 Jan. 2007 (AS 2006 4287; BBl 2005 937).
Art. 24 Storage in man-made caverns
Liquids which may pollute water may not be stored in underground caverns if they come into contact with groundwater as a result of such storage.
Art. 25 Substances which may form liquids which may pollute water
Articles 22 and 24 apply by analogy to substances which when mixed with liquids may form liquids which may pollute water.
Art. 26
Repealed by No I of the FA of 24 March 2006, with effect from 1 Jan. 2007 (AS 2006 4287; BBl 2005 937).
Section 6 Soil Use and Measures applying to Waters
Art. 27 Soil use
1 Soils shall be used according to the state of the art, in such a way that waters are not adversely affected in any way, in particular avoiding both washing away and leaching of fertilisers and plant treatment products. 1bis In the area of contribution of drinking water wells, only plant protection products whose use does not lead to groundwater concentrations of active substances and degradation products exceeding 0.1 µg/l may be used. 2 The Federal Council may enact the necessary regulations.
Para. 1bis — Inserted by No I 2 of the FA of 19 March 2021 (Amendment of the Chemicals Act, the Waters Protection Act and the Agriculture Act), in force since 1 Feb. 2023 (AS 2022 263; 2023 2; BBl 2020 6523, 6785).
Art. 28 Measures applying to waters
If the measures contained in Articles 7–27 prove insufficient to maintain the water quality requirements (Art. 9 para. 1) for a specific body of water, the cantons shall ensure that additional measures shall be applied to the body of water itself.
Chapter 2 Ensuring appropriate Residual Flow
Art. 29 Permits
A permit is required by any person who, over and above normal public use: a. withdraws water from a watercourse with permanent flow; b. withdraws water from lakes or groundwater resources in such a way as to affect substantially the discharge rate of a watercourse with permanent flow.
Art. 30 Conditions for the permit
Such withdrawal may be permitted provided that: a. the requirements contained in Articles 31–35 are complied with; b. taken together with other withdrawals, the flow rate Q347 is reduced by at most 20 per cent and total withdrawal amounts to not more than 1,000 litres per second; or c. for the supply of drinking water, at most 80 litres per second from a spring and at most 100 litres per second from groundwater, based on the annual average, is withdrawn.
Art. 31 Minimum residual flow
1 When withdrawal takes place from a permanently flowing watercourse, the minimum residual flow must be as follows: up to a flow rate Q347 of 60 l/s 50 l/s and for each further 10 l/s of flow rate Q347 8 l/s , for a flow rate Q347 of 160 l/s 130 l/s and for each further 10 l/s of flow rate Q347 4.4 l/s more, for 500 l/s of flow rate Q347 280 l/s and for each further 100 l/s of flow rate Q347 31 l/s more, for 2,500 l/s of flow rate Q347 900 l/s and for each further 100 l/s of flow rate Q347 21.3 l/s more, for 10,000 l/s of flow rate Q347 2,500 l/s and for each further 1000 l/s of flow rate Q347 150 l/s more, from 60,000 l/s of flow rate Q347 10,000 l/s . 2 The minimum residual flow calculated according to paragraph 1 above shall be increased if the following requirements are not complied with and cannot be complied with as a result of other measures: a. The prescribed water quality of the surface waters must be maintained in spite of the water withdrawal and existing wastewater discharg
Art. 32 Exceptions
The cantonal authorities may lay down lower minimum residual flow rates in the following circumstances: a. if the flow rate Q347 of the body of water is lower than 50 l/s: over a 1,000 m long stretch below a point of withdrawal from a body of water situated at an altitude higher than 1,700 m above sea level or from a body of water not suitable as a habitat for fish and situated at an altitude between 1,500 and 1,700 m above sea level; b. in the case of water withdrawals from bodies of water not suitable as habitats for fish provided that the residual rate of flow represents at least 35 per cent of the flow rate Q347; bbis. on a 1000 m long stretch below a place of withdrawal in sections with negligible ecological potential, provided the natural functions of the body of water are not substantially impaired; c. in the framework of a protection and utilisation planning for a limited area forming a topographical whole, in so far as an appropriate balance can be achieved in the same area by
let. a — Amended by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079). let. bbis — Inserted by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079).
Art. 33 Increase of the minimum residual flow
1 The authorities shall increase the minimum residual flow to the extent which is deemed necessary after weighing up the interests for and against the planned water withdrawal. 2 Interests in favour of a water withdrawal are as follows: a. public interests which may be served by the water withdrawal; b. economic interests of the area in which the water originates; c. economic interests of those wishing to withdraw the water; d. energy supply which may be served by the water withdrawal. 3 Interests against a water withdrawal are as follows: a. the significance of the waters as an element of the landscape; b. the significance of the waters as a natural habitat and for the conservation of the diversity of the dependent fauna and flora, in particular of the fish fauna, the income derived from fishing and the natural reproduction of fish; c. maintaining a rate of flow sufficient to satisfy the quality requirements of waters in the long run; d. maintaining a balanced groundwater regimen whic
Art. 34 Water withdrawal from lakes and groundwater resources
If water is withdrawn from lakes or groundwater resources and the rate of flow of watercourses is thereby substantially affected, the watercourses in question must be protected as provided for in Articles 31–33.
Art. 35 Decision of the authorities
1 The authorities shall decide in each individual case on the required water endowment and any other measures which may be necessary to protect waters below the point of withdrawal. 2 They may specify temporally variable required water endowments. Residual flows shall not fall below those specified in Articles 31 and 32. 3 The authorities shall consult the competent agencies before making their decision; in cases where the withdrawals in question concern hydropower plants with gross production in excess of 300 kW, they shall also consult the federal government.
Art. 36 Control of the required water endowment
1 Anyone withdrawing water from any body of water shall be required to prove to the authorities by means of measurements that he will maintain the required water endowment. If the cost of such a procedure is unreasonable, evidence may be provided by a calculation based on the water balance. 2 If he proves that the effective rate of flow is temporarily lower than the required water endowment, he is only obliged to maintain a required water endowment equal of the effective rate of flow during the period in which such a situation exists.
Chapter 3 Prevention and Remediation of other Detr
Amended by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079).
Art. 36a Space provided for waters
1 The cantons, after hearing the parties concerned, shall stipulate the spatial requirements for surface waters (space provided for waters) in order to guarantee the following functions: a. the natural functions of the waters; b. flood protection; c. the use of the waters. 2 The Federal Council shall regulate the details. 3 The cantons shall ensure that that space provided for waters is taken into account in structure and land use planning and that it is developed and exploited extensively. The space provided for waters does not constitute arable land. In the event of a loss of arable land, this must be compensated for as specified in the federal sectoral plan in accordance with Article 13 of the Spatial Planning Act of 22 June 1979.
Art. 36a — Inserted by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079). Para. 3 — SR 700
Art. 37 Operations on surface waters
1 Surface waters may only be channelled or straightened if: a. it is necessary for flood protection (Art. 3 paras 1−3 of the Hydraulic Engineering Act of 21 June 1991); b. it is necessary for the provision of a navigable passage or for the use of hydropower that is in the public interest; c. it is necessary for the construction of a landfill that can only be constructed at the planned location and in which only unpolluted excavation material or spoil is deposited; or d. the condition of an already channelled or straightened body of surface water can be improved in terms of this Act. 2 In the event of operations on surface waters, the natural course of the body of water must as far as possible be preserved or restored. 3 Surface waters and the space provided for waters must be developed and maintained in such a manner that: a. they provide a habitat for diversified fauna and flora; b. the interactions between surface and underground waters are maintained to the greatest extent possible;
Art. 37 — Amended by Annex No 4 of the FA of 15 March 2024, in force since 1 Aug. 2025 (AS 2025 430; BBl 2023 858). Para. 1 let. a — SR 721.100
Art. 38 Covering and culverting of watercourses
1 Watercourses may not be covered or culverted. 2 The authorities may permit exceptions for: a. flood overflow and irrigation channels; b. passages under traffic ways; c. passages under agricultural or forestry transport routes; d. small drainage channels with intermittent flow; e. the replacement of existing underground passages or coverings, insofar as an open watercourse is not possible or would put substantial disadvantages in the way of agricultural utilisation.
Art. 38a Rehabilitation of waters
1 The cantons shall ensure that waters are rehabilitated. In doing so, they take account of the benefits to nature and the landscape as well as the economic consequences of the rehabilitation. 2 They shall plan the rehabilitation measures and specify the time schedule therefor. They shall ensure that these plans are taken into account in the structure and land use planning. In the event of a loss of arable land, this must be compensated for as specified in the federal sectoral plan in accordance with Article 13 of the Spatial Planning Act of 22 June 1979.
Art. 38a — Inserted by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079). Para. 2 — SR 700
Art. 39 Introduction of solid substances into lakes
1 The introduction of solid substances into lakes is prohibited even in cases where these substances would not lead to pollution. 2 The cantonal authorities may permit the creation of embankments: a. for the construction of buildings in built-up areas which cannot be located elsewhere if an overriding public interest requires such an embankment and the purpose in view cannot be attained in any other way; b. if a shallow water zone may be thereby improved. 3 The embankments created shall be as natural as possible, and all bank flora destroyed shall be replaced.
Art. 39a Hydropeaking
1 Those responsible for hydropower plants must prevent or eliminate by means of civil engineering measures short-term artificial changes in the water flow on a body of water (hydropeaking) that cause serious harm to the indigenous flora and fauna as well as their habitats. At the request of the person responsible for a hydropower plant, the authority may order operational instead of civil engineering measures. 2 The measures are determined by: a. the degree of harm caused to the body of water; b. the ecological potential of the body of water; c. the proportionality of the cost; d. the interests of flood protection; e. the energy policy goals relating to the promotion of renewable energy sources. 3 Within the catchment area of the body of water concerned, the measures must be coordinated with each other after hearing the persons responsible for the hydropower plants concerned. 4 Retention basins constructed in application of paragraph 1 may be used for pumped storage without modificatio
Art. 39a — Inserted by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079).
Art. 40 Flushing out and emptying of impoundments
1 The person responsible for a dam shall as far as possible ensure that in flushing or emptying an impoundment or when inspecting drainage and flood overflow structures, downstream fauna and flora are not harmed. 2 Flushing and emptying shall take place only with the authorisation of the cantonal authority. The licensing authority shall consult interested specialist agencies. If periodical flushing and emptying are required in order to maintain operational safety, the authority shall fix only the times and types of such operations. 3 If a person responsible is obliged to lower the water level of a reservoir on safety grounds as a result of exceptional events, he shall immediately inform the responsible authority.
Art. 41 Flotsam at dams
1 Anyone who dams up a watercourse may not put any flotsam which he may have removed for operational reasons back into the water. The authority may grant exceptions. 2 The person responsible for a dam must periodically collect the flotsam near his installation according to the instructions of the authority.
Art. 42 Withdrawal and discharge of fresh water or used water
1 If water is withdrawn from or discharged into a natural lake, the stratification and flow conditions in the lake may not be substantially modified, and no water-level fluctuations potentially harmful to the riparian zone may be allowed to occur. 2 In the case of watercourses, the type and location of the discharge of fresh water or wastewater must be selected in such a way that as little artificial reinforcement and correction as possible is required.
Art. 43 Conservation of groundwater resources
1 The cantons shall ensure that over the long term no more water is withdrawn from groundwater resources than flows into them. In the short term, more water may be withdrawn unless this impairs the quality of groundwater or the vegetation. 2 If a groundwater resource is impaired as a result of excessive withdrawal or through reduced recharge, the canton shall ensure that the situation is remedied as far as possible, either through reducing the rate of withdrawal or by artificial recharge or by underground storage of drinking water. 3 Different groundwater resources may not be connected to each other on a permanent basis if such a connection may impair the quantity or quality of the groundwater. 4 Storage volumes and flows of usable groundwater resources may not be substantially reduced on a permanent basis as a result of new installations of any kind. 5 Low dams shall not substantially impair the groundwater nor the vegetation which depends on the groundwater level. The authority may g
Art. 43a Bed load budget
1 The bed load budget in the body of water may not be changed by installations to the extent that they cause serious harm to the indigenous flora and fauna, their habitats, the groundwater regimen and flood protection. The persons responsible for the installations shall take suitable measures to this end. 2 The measures are determined by: a. the degree of harm caused to the body of water; b. the ecological potential of the body of water; c. the proportionality of the cost; d. the interests of flood protection; e. the energy policy goals relating to the promotion of renewable energy sources. 3 Within the catchment area of the body of water concerned, the measures must be coordinated with each other after hearing the persons responsible for the installations concerned.
Art. 43a — Inserted by No I of the FA of 11 Dec. 2009 (Restoration), in force since 1 Jan. 2011 (AS 2010 4285; BBl 2008 8043 8079).
Art. 44 Extraction of gravel, sand and other materials
1 Anyone wishing to extract gravel, sand or other materials or to carry out preparatory excavations for such extraction requires a permit. 2 Permits for such work may not be granted: a. in groundwater protection zones; b. below the groundwater table of groundwater resources whose amount and quality are suitable for water supply; c. for watercourses where the bed load budget may be negatively affected. 3 For groundwater resources whose amount and quality are suitable for water supply, extraction may be permitted above groundwater level, provided a protective layer of material is left above the maximum groundwater table possible. The dimension of this protective layer shall be chosen according to the local conditions.