In relation to the subject of poisoning water resources as a method of warfare in the CW.
Believe there were isolated, albeit rare, incidents of both sides dumping animal carcasses into ponds to deliberately poison the water supply.
For example. Following the surrender of Vicksburg and the deployment of Sherman to Jackson, Sherman refers to a poisoning incident by retreating Confederates when he wrote in his memoirs:-
…"The next day (July 4, 1863) Vicksburg surrendered, and orders were given for at once attacking General Johnston. The Thirteenth Corps (General Ord) was ordered to march rapidly, and cross the Big Black at the railroad-bridge; the Fifteenth by Mesainger's, and the Ninth (General Parker) by Birdsong's Ferry-all to converge on Bolton. My corps crossed the Big Black during the 5th and 6th of July, and marched for Bolton, where we came in with General Ord's troops; but the Ninth Corps was delayed in crossing at Birdsong's. Johnston had received timely notice of Pemberton's surrender, and was in full retreat for Jackson. On the 8th all our troops reached the neighborhood of Clinton, the weather fearfully hot, and water scarce. Johnston had marched rapidly, and in retreating had caused cattle, hogs, and sheep, to be driven into the ponds of water, and there shot down; so that we had to haul their dead and stinking carcasses out to use the water."….
(Source:
MEMOIRS OF GENERAL SHERMAN, COMPLETE (gutenberg.org) See Chapter XIII)
Also, in relation to any practice of poisoning. The Union War Department issued General Orders No. 100 on April 24, 1863 (known as 'The Lieber code of 1863') regulating the conduct of Union armies in the field. Of particular note, was article 16 of Section 1, which provided in part:-
16. Military necessity does not admit of cruelty--that is, the infliction of suffering for the sake of suffering or for revenge, nor of maiming or wounding except in fight, nor of torture to extort confessions. It does not admit of the use of poison in any way, nor of the wanton devastation of a district.
(Source:
http://www.civilwarhome.com/liebercode.htm )
Am unaware of any corresponding formal regulation by the Confederacy for its armies in the field.