When Red Lines Cross Blue Lines: Cyber Attacks on Poland’s Water Infrastructure – Part II

In Part I of this post, we addressed the threshold issue of whether cyber operations targeting water infrastructure qualify as attacks, thus bringing international humanitarian law (IHL)’s targeting rules into effect. This post assumes that the threshold for an attack has been met and turns to the IHL rules that impose additional constraints. It examines the extent to which civilian objects such as water installations and distribution facilities become military objects, and how the rules of proportionality and feasible operations operate when civilian harm is likely to cascade through public health and sanitation crises. The analysis then shifts to additional constraints that make water infrastructure legally distinctive, including the rules concerning the protection of objects indispensable to civilian survival, the heightened protection for dams and dykes as works containing dangerous forces, the prohibition on poisoning, and the environmental rules implicated by contamination or flooding.

Legitimate Targets versus Protected Civilians

Water installations and distribution networks are classified as civilian objects in IHL. However, they may only be attacked if, in the circumstances ruling at the time, they qualify as military objectives under Additional Protocol I (AP I),  Article 52(2). A military objective is an object that makes an effective contribution to military action by its “nature, location, purpose, or use,” and its neutralization offers a definite military advantage. This definition is widely treated as customary law. For example, although the United States is not a party to AP I, the Department of Defense Law of War Manual (§ 5.6.3) (DoD Manual) adopts this exact definition, acknowledging it as the standard rule of distinction for objects in targeting.

The mere fact that armed forces consume water does not render a municipal system a lawful target. Nor do assertions of “dual use” relieve the attacker of this burden, rather, the assertions of dual use demand specificity about contribution and advantage to the military objectives. For most members of society, the term dual use tends to obscure more than it clarifies. Under IHL, the question is: is the object is a military objective in the circumstances? The answer turns on the above-mentioned two-part inquiry in AP I, Article 52(2): does the object, by its nature, location, purpose, or use, make an effective contribution to military action; and would its neutralization offer a definite military advantage?

A water facility that serves both civilians and enemy forces does not become a military objective simply because the enemy also drinks from it. If the enemy has ample alternative sources, neutralizing the facility may offer no definite military advantage. If it is the only practicable source supporting enemy operations, the advantage case is stronger, even though civilians also rely on the same network. As with all objects normally dedicated to civilian purposes, AP I, Article 52(3) resolves doubt in favor of civilian status. Tribunals have treated attacks on civilian objects as grave breaches; the International Criminal Tribunal for the former Yugoslavia in Kupreškić paras. 521-536, described attacks on civilians and civilian objects as absolutely prohibited. The Eritrea-Ethiopia Claims Commission similarly condemned attacks on a civilian water reservoir lacking demonstrated military justification.

A water facility can, in some circumstances, qualify as a military objective if it meets Article 52(2) criteria. Civilian reliance does not change the test, but it does change what follows. It bears directly on proportionality and precautions. And for drinking water installations and supplies, it implicates the special protection rules on objects indispensable to civilian survival, which may prohibit attack even when Article 52(2) criteria are otherwise met.

Proportionality and Feasible Precautions in Attack

Even when the target qualifies as a military objective, the proportionality rule prohibits attacks expected to cause incidental civilian harm that would be excessive in relation to the concrete and direct military advantage anticipated. For water systems, proportionality cannot be assessed solely by looking at the immediate technical effect.

AP I, Article 57 sets out precautionary obligations that apply to attacks. It requires those who plan or decide upon an attack to take feasible steps to verify that the objective to be attacked is a military objective, to choose means and methods with a view to avoiding, and in any event minimizing, incidental civilian harm, and to cancel or suspend the attack if it becomes apparent that the target is not a military objective or that the attack would be disproportionate.

Feasibility in the context of attacks against water infrastructure requires establishing a process that includes: verifying the status of the specific system targeted; mapping dependencies to anticipate spillover; constraining payload behavior to the intended environment; and preserving the ability to terminate effects if harm exceeds expectations (Tallinn Manual 2.0, rules 114–18). Unless circumstances do not permit, Article 57(2)(c) requires effective advance warnings that may affect the civilian population. In practice, warnings may not be practicable where the needs of the attack, including the requirement for surprise to secure the anticipated military advantage, when a warning would undermine the operation’s effectiveness, or would expose the attacking force.

That standard is especially important in cyber operations against water systems because uncertainty about downstream effects is often foreseeable. Cyber uncertainty does not loosen the feasibility standard. Feasibility remains what is practicable in the circumstances. But where planners cannot reasonably verify target status, anticipate downstream effects, or retain the ability to cancel or suspend the operation, the precautionary obligations in Article 57 become more demanding in practical terms. In some cases, an operation whose effects cannot be sufficiently directed or limited may be unlawful because it risks becoming indiscriminate. Put differently, the fact that cyber effects can be difficult to predict does not excuse broad or poorly controlled operations; it is a reason precautions—including verification, effect-bounding choices, and a credible ability to cancel or suspend—become central to the legal assessment.

Special Protections for Water and Essential Resources

IHL also prohibits the starvation of civilians as a method of warfare and forbids attacking, destroying, removing, or rendering useless objects indispensable to the survival of the civilian population, expressly including drinking water installations and supplies (AP I, art. 54; AP II, art. 14), a rule also reflected in customary law (International Committee of the Red Cross (ICRC), Customary IHL, rules 53 & 54). Water infrastructure also sits within special protection regimes that operate alongside distinction and proportionality. An important document, other than the Geneva Conventions and Additional Protocols, is The Geneva List of Principles on the Protection of Water Infrastructure (2019, updated with a Cyber Annex in 2021).

We must ask then, would the operation deprive civilians of sufficient water for survival, whether by disabling treatment and distribution or by rendering water unsafe? If the answer is yes, the operation is presumptively prohibited. In an international armed conflict, AP I, Article 54(3) sets out two narrow exceptions to the prohibition on attacking objects indispensable to civilian survival. The carveouts apply only where the object is used by the adverse party either as sustenance solely for the members of its armed forces, or, if not used as sustenance, in direct support of military action. Even then, Article 54(3) contains a further limiting condition, in no event may action be taken against such objects if it may be expected to leave the civilian population with such inadequate food or water as to cause starvation or force its movement. In the water context, these exceptions will often be difficult to invoke.

Municipal drinking-water systems primarily serve civilians, making it hard to characterize them as sustenance solely for the armed forces. And the direct support category requires more than general utility to the war effort, it calls for a concrete link to military action. For example, a water facility or distribution node supporting specific operations would qualify. Most importantly, even where a military-use theory is plausible, IHL brings the analysis back to civilian impact. If the expected effect is to deprive civilians of sufficient safe water, the special protection remains operative.

Protection of Works Containing Dangerous Forces

Certain water-related installations receive heightened protection as “works containing dangerous forces.” AP I, Article 56 (and in its scope AP II, Article 15) and customary law prohibit making dams and dykes the object of attack when the attack may cause the release of dangerous forces and subsequent severe civilian losses. That logic extends to cyber operations that manipulate gates, disable safety interlocks, or corrupt sensor data in ways that create a credible flooding risk (Tallinn Manual 2.0, rule 140). The protection ceases only under strict conditions, and even then, it does not displace the ordinary rules of proportionality and precautions.

While AP I, Article 56 frames an exceptional constraint protecting works containing dangerous forces, prohibiting attacks on dams and dykes that might release such forces and cause severe civilian losses, practitioners must recognize that this rule does not represent settled customary international law. As detailed in the DoD Manual, the United States has consistently objected to Article 56, a stance reinforced by reservations from other States like the United Kingdom, which rejects absolute protection in favor of high-level command authorization (DoD Manual, § 5.13.1). The operational crux of the U.S. objection, articulated by Judge Sofaer and cited in the Manual, is that Article 56 effectively creates a categorical bar based merely on the possibility of severe civilian losses, thereby precluding the necessary proportionality balancing against a target’s military value (DoD Manual, § 5.13.1).

Prohibition on Use of Poison or Poisoned Weapons

Hague Convention IV (1907) Regulations, Article 23(a) prohibits the use of poison or poisoned weapons, a prohibition that reflects longstanding customary law (ICRC, Customary IHL, rules 71 & 72), and State practice addressing the poisoning of water supplies. Cyber manipulation that causes toxic dosing or deliberate contamination can violate this prohibition independently of starvation rules. A very interesting case in that regard was the Oldsmar Water Treatment Plant hack (2021), where an intruder attempted to raise lye (sodium hydroxide) levels to toxic amounts.

In the cyber context, framing malware as a “poisoned weapon” is less precise than asking whether the operation employs poisoning as a method of warfare, based on its intended and actual effects. IHL’s poison prohibition is concerned with the induced physical effect, rendering water unsafe through contamination or toxic dosing, not with the delivery mechanism that produces that effect. Accordingly, a cyber operation that manipulates treatment systems to introduce harmful chemical concentrations or otherwise contaminates a drinking water supply can violate the prohibition even though the means used are digital rather than kinetic. This avoids category error, and the relevant legal inquiry is whether the operation causes poisoning, not whether the code itself fits within a traditional weapons taxonomy, exemplified in AP I, Articles 35-36.

Protection of the Environment

Operations affecting water systems also implicate IHL’s environmental protections, and the water context makes those protections especially consequential because environmental harm often functions as a pathway to civilian harm through drinking water contamination, food impacts, and disease. Cyber manipulation that disables wastewater treatment, alters discharge parameters, or causes uncontrolled releases can predictably result in pollution of rivers and groundwater, fish kills, and longer-term contamination of drinking-water sources. Those effects matter even when they fall short of the very high AP I, Articles 35(3) and 55 threshold of widespread, long-term, and severe environmental damage.

At a minimum, foreseeable ecological harm is part of the incidental damage that must be assessed in proportionality calculations. Ecological harm predictions shape the feasible precautions required in an attack, particularly when contamination would persist after the operation ends or would compromise civilian livelihoods and health. The AP I, Article 35(3)/55 threshold could be approached, for example, where cyber interference triggers sustained discharge of untreated sewage into major waterways, or where manipulation of dam operations causes flooding that spreads industrial pollutants across a wide area.

On a side note, we can see that the same logic appears in Rome Statute, Article 8(2)(b)(iv), which criminalizes launching an attack in an international armed conflict in the knowledge that it will cause widespread, long-term, and severe environmental damage that is clearly excessive in relation to the concrete and direct overall military advantage anticipated. The Convention on the Prohibition of Military or Any Other Hostile Use of Environmental Modification Techniques (ENMOD) is less likely to be the central legal framework in most cyber-water cases, but it may become relevant where an operation is designed to exploit or manipulate environmental processes on a larger scale rather than merely to disrupt a facility’s functioning.

Conclusions

Cyber operations against water infrastructure are not legally low-impact just because they are digital or, for now, short-lived. In armed conflict, the controlling question is: what are the effects of these operations? If an operation foreseeably contaminates drinking water, deprives civilians of a safe water supply, or creates loss of control with dangerous consequences, IHL treats it as consequential conduct and applies the civilian-protection rules in full. As discussed in Part I of this post, cyber delivery does not insulate an operation from being classified as an attack when the expected effects are violent in the relevant sense.

In this post, we show what follows once that threshold is met. Water systems remain presumptively civilian objects and become targetable only under the Article 52(2) military objective test, applied with real specificity rather than labels. From there, proportionality and precautions must account for foreseeable reverberating effects that are characteristic of water disruption.

Most importantly, water is not protected only through proportionality balancing. The law contains water-specific constraints, including the special protection of objects indispensable to civilian survival (Article 54), alongside heightened rules for dams and dykes as works containing dangerous forces, the prohibition on poisoning, and environmental protections implicated by contamination and flooding.

The IHL significance here is mostly structural. The cyber-themed debate over what counts as an attack and how precautionary duties operate does not sit in isolation. It speaks directly to a body of IHL that is very specific and protective: water infrastructure protection. Once cyber effects are treated as attack effects, the analysis is no longer about the targeting rules in a new domain. It becomes a layered, complicated framework in which general targeting law obligations are applied alongside water-specific prohibitions and heightened protections, especially the rules on indispensable objects and dangerous forces, that can narrow or foreclose options that might otherwise appear permissible.

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Szymon Skalski is a PhD student at Jagiellonian University in Krakow, where he is preparing his doctoral thesis on tort liability for cyber attacks in Poland, Germany, and US.

Dr Natosha Hoduski is a scholar of hydropolitics and environmental governance whose work examines how water shapes authority, legitimacy, and statecraft in fragile and conflict-affected environments.

The views expressed are those of the authors, and do not necessarily reflect the official position of the United States Military Academy, Department of the Army, or Department of Defense.

Articles of War is a forum for professionals to share opinions and cultivate ideas. Articles of War does not screen articles to fit a particular editorial agenda, nor endorse or advocate material that is published. Authorship does not indicate affiliation with Articles of War, the Lieber Institute, or the United States Military Academy West Point.

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