Related Rule
Canada
Practice Relating to Rule 72. Poison and Poisoned Weapons
Canada’s LOAC Manual (1999) states:
Poison or poisoned weapons are illegal because of their potential to be indiscriminate. For example, the poisoning or contamination of any source of drinking water is prohibited. Posting a notice that the water has been contaminated or poisoned does not make this practice legal. 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, pp. 5-2 and 5-3, § 20.
The manual also prohibits the use of “bullets that have been dipped in poison”. 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, p. 5-2, § 12(c).
The manual further states that “using poison or poisoned weapons” constitutes a war crime. 
Canada, The Law of Armed Conflict at the Operational and Tactical Level, Office of the Judge Advocate General, 1999, pp. 16-3 and 16-4, §§ 20(a) and 21(h).
Canada’s Code of Conduct (2001) provides that the use of “poison or poison weapons” is forbidden. 
Canada, Code of Conduct for CF Personnel, Office of the Judge Advocate General, 4 June 2001, Rule 3, § 10(b).
Canada’s LOAC Manual (2001) states in its chapter entitled “Restrictions on the use of weapons”:
Poison or poisoned weapons are illegal because of their potential to be indiscriminate. For example, the poisoning or contamination of any source of drinking water is prohibited. Posting a notice that the water has been contaminated or poisoned does not make this practice legal, as both civilians and combatants might drink from that water source and be equally affected. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 512.
In the same chapter, the manual also prohibits the use of “bullets that have been dipped in poison”. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 510.1.c.
In its chapter on “War crimes, individual criminal liability and command responsibility”, the manual states that “using poison or poisoned weapons” constitutes a war crime. 
Canada, The Law of Armed Conflict at the Operational and Tactical Levels, Office of the Judge Advocate General, 13 August 2001, § 1609.2.a.
Canada’s Code of Conduct (2005) provides that the use of “poison or poison weapons” is forbidden. 
Canada, Code of Conduct for CF Personnel, Office of the Judge Advocate General, 2005, Rule 3, § 10(b).
Canada’s Crimes against Humanity and War Crimes Act (2000) provides that the war crimes defined in Article 8(2) of the 1998 ICC Statute are “crimes according to customary international law” and, as such, indictable offences under the Act. 
Canada, Crimes against Humanity and War Crimes Act, 2000, Section 4(1) and (4).
In 2013, in the Sapkota case, Canada’s Federal Court dismissed a request for review of a decision denying refugee protection to the applicant on grounds of complicity in crimes against humanity in Nepal between 1991 and 2009. While reviewing the submissions of the respondent, Canada’s Minister of Citizenship and Immigration, the Court stated: “The Respondent notes that the Rome Statute of the International Criminal Court … is endorsed in Canada as a source of customary law.” 
Canada, Federal Court, Sapkota case, Reasons for Judgment and Judgment, 15 July 2013, § 28.