Safety of the use of alum in water to be used for consumption

Hi, Judy. You probably aren't asking quite the right people because this is a metal finishing site, not a domestic water treatment site. But aluminum sulphate is used in water treatment plants to clarify drinking water, so I guess it's safe in a lake.

As for its ability to kill weeds, I hadn't heard that before; I had only heard of copper sulphate ⇦ this on eBay or Amazon [affil links] for that job.

Up until at least 1998, our company a large Fortune 40 was using ferric chloride as a precipitant in a waste water treatment facility permitted under Ohio EPA meeting US Federal RPA standards for wastewater. We were being approached to change from ferric chloride to alum to reduce the amount of iron in the water. Sulfuric acid is used to adjust pH before disposal of the water into a pipe going to a wastewater facility and is considered safe for drinking water. Without direct knowledge, the best that can be said is that in dilute concentrations this is probably okay. Another alternative is the addition of other biocides like copper sulphate nicknamed blue rock. I prefer the aluminum rather than copper ions. You can also use silver nitrate which is a whole lot less desirable than alum. Your concern may be about the aluminum. Years ago a Canadian study frappe'd the brains of Alzheimer's patients and found high levels of aluminum. So they concluded aluminum caused Alzheimer's. Now we know that everyone's brain has high levels of aluminum. Go to the web page for Calphalon hard anodized aluminum to find this information. It turns out the best precipitant is likely colloidal silica that is just SiO2. Entirely safe. Just expensive.

I've never understood why some POTWs are opposed to industrial pre-treaters employing iron as their co-precipitant, Dave, although they probably have their reasons. One of the advantages of iron is that it is rarely overdosed because it is very visible if it is, whereas aluminum remains invisible at dosage rates that are way more than needed. Of course, it is understandable that a municipal water treatment facility would not want to use a clarification aid that becomes visible if they put too much in :-)

Ted Mooney, P.E.
Striving to live Aloha
finishing.com - Pine Beach, New Jersey
2003

Ms. Braiman,

Please verify that aluminum sulphate is the proposed chemical. Garden shops sell it as a soil acidifier for plants such as azaleas and blueberries: "To make hydrangeas blue, give them a monthly application of aluminum sulphate." It is also a general-purpose food additive. I doubt it will be an effective herbicide except at enormous doses giving an acidic, saltwater lake.