Using bleach for other water purfication purposes

[JimB]

I wasn't sure where to post this, so if it would be better somewhere else in the forum let me know.

Our city's water treatment plant has been have some issues going on seven days know. We've been under a boil alert since last Friday evening. I won't go into details of what's been reported as the reason for the boil alert unless someone wants more info. The mayor and water dept says the turbidity level and baterial levels have been at or less than the approved amounts but the EPA will not certify them. (There are other issues such as notification, or lack of notification, to the citizens. I've been buying store brand drinking water since this began.

I am using city water for showers and doing laundry. My question concerns washing dishes. I can't get an answer from the city if a dishwasher's drying cycle would be hot enough to sterilize dishes even if the bateria level would be somewhat high. That's a moot point for me, anyway, because I am the dishwasher. Three days ago I decided to boil enough water to fill both sink basins and wash dishes. Boiling enough water took a bit over an hour but it took close to four hours for the water to cool enough for me to wash the dishes. Since we use bleach to sanitize our pools, would that be ok for sanitizing water to wash dishes? I found a couple websites dealing with using bleach for drinking water in emergency conditions and they call for 1/8 teaspoon per gallon.

Thought?

 

[mpacheco72]

I don't see why not. I have used bleach in my dish water before.

 

[chem geek]

If you mean creating a mild bleach solution in your sink in order to soak/wash the dishes, then yes that would readily disinfect them and more importantly would quickly kill whatever was in the city water. 1/8 teaspoon of 6% bleach per gallon would be 10 ppm FC. That is way more than needed to kill bacteria, but chlorine will get used up with food particles so you'll want to make sure to rinse or wash the plates first before soaking/dipping them in the chlorinated waster.

However, soap and water do a good job of getting most of the pathogens off the dinnerware and do kill a lot of them (though not as quickly or thoroughly as bleach) so your dishwasher with its detergent should do a decent job anyway. The heat in drying is probably not enough to kill everything (i.e. it's not sterilization), but between the dishwashing detergent and the heat you're probably OK. We're not talking sewage anyway and it sounds like their bacterial counts are low. As described in this link, the Maximum Contaminant Level (MCL) for the Hetertrophic Plate Count (HPC) is 500 CFU/ml while for Total Coliforms it is 5% (i.e. 95% of samples must show zero) and if Total Coliforms are detected then either fecal coliforms or E.coli must be tested and if not zero then this is an acute MCL violation.

Note that you do NOT use bleach in your dishwasher directly since that would be too strong and isn't good for the metals and rubber in the dishwasher. There isn't any way to slowly feed bleach into the water going into the dishwasher to simulate chlorinated water.

 

[mpacheco72]

It was my understanding that most dishwasher detergents contained bleach anyway.

 

[chem geek]

You are right. I checked the MSDS for Cascade Powder which has sodium carbonate, sodium silicate and 0.5-1.5% Dichlor. Cascade Gel has sodium carbonate, sodium silicate, 0.5-1.5% bleach, sodium hydroxide.

Bosch dishwashers are very energy and water efficient using only 2 gallons of water. It uses a minimum of 15 ml of detergent. That correlates to about 1.2 ppm FC from bleach, but 11 ppm FC from Dichlor, though moderated in strength by CYA so similar to 3.8 ppm FC. So this is within the range of what is found in chlorinated tap water.

 

[mpacheco72]

My understanding is that most residential dishwashers don't actually get hot enough to kill germs and so most dishwasher detergents add bleach to make sure they do an effective job.

 

[dschlic1]

Many water departments are now using bleach to sanitize their water. Used to be chlorine gas, however most have changed over for material safety reasons. Also an important trend is the usage of chlorimines as a santizer.