War Water, a.k.a Water of Mars, Iron Water.

Rarely has such a simple formula captured the imagination and endured through time. While there is evidence to suggest that it was once used by folk healers as a treatment for anemia, the most common modern usage involves cursing. Protection, reversals, and placement. For those of you who have the Rede stuck up your butt, I will say this: It isn't the tool at fault, but how it is utilized with the application of intent that determines karmic repercussions. "Harm None" includes yourself, and allowing yourself to be a psychic punching bag is not healthy. I know the idea might make your skin crawl, so before you grab a sage bundle and wave it at your computer, allow me to cover the more benign aspects of War Water.

Protection
War Water works like turpentine, stripping away any psychic garbage that's built up in your aura. An excellent cleanser, I use it in the bath when I feel my defenses are low due to stress, overwork, or illness. Nature abhors a vacuum, so be sure to fill the empty space with something positive after a purification! War Water is great for physical structures as well, or to use in asperging your circle, especially with protection-focused rituals.

Reversals
Sending malevolent energy back to its source. Intentionally focused, magically generated curses are fairly rare, especially compared to the level of paranoia about them. More often than not, when you feel "cursed" it is a combination of negative thoughts directed towards you acting as a catalyst, which you then feed with your own energy. Believing you are cursed has a powerful affect on your mental and emotional state, which then translates itself into a perception of "luck". Boss passes you over for that promotion because he sees you as jumpy, skittish, or distracted; you catch every red light on the way home, break the good china, fight with your lover. When nothing seems to be going your way, cleansing is in order. If you are positive beyond a doubt that you have been cast on, however, bouncing the negative energy back to its source is within your rights. Specifying "back to the source" when doing a reversal insures that innocent bystanders don't get slammed. You may have your suspicions about who threw the hex, but they are just that: suspicions.

Cursing
War water is reputed to have the power to create strife, discord and all around trouble when used in a curse. Traditionally, it was thrown at the victim's home, creating both psychological and magical torture, especially if they were an experienced magician and know what the broken glass and iron/ sulfurous smell meant.
Really heavy duty stuff, a traditional component in "witch wars". Though I wouldn't encourage you to run around throwing curses for any petty reason, the fact remains that they are occasionally necessary. I will trust your best judgment and discrimination in using this product ethically.