Product review (5 stars): You need a bacteriostat!
If you use a humidifier--especially one that uses a wick--you need this. After my first winter of using my&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/Holmes-Smart-Humidifier/dp/B00KL770Z0/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">Holmes Smart Humidifier</a>, I checked the wick/filter, and it was pretty disgusting. Some form of fungi or bacteria had built up, and one assumes the air blown into the room contained those spores or bacteria. My humidifier was running quite a bit last winter, and I found myself refilling the relatively large reservoirs every few days. This means that a very large volume of air was being moved through the wicks, so that toward the end of winter a lot of bacteria was being distributed in my house.  The addition of a small amount of bacteriostat to each refill of the tanks solves this problem.

Being summer as of this writing, I find that I need a dehumidifier instead (I use a humidifier during winter and a dehumidifier during the summer in my finished basement). I had been using&nbsp;<a data-hook="product-link-linked" class="a-link-normal" href="/BestAir-Bacteriostatic-Treatment/dp/B000CMHLMG/ref=cm_cr_arp_d_rvw_txt?ie=UTF8">BestAir Bacteriostatic Treatment</a>, which has an almost identical ingredients list on the label. If nothing else is different, however, the price of this Sunbeam brand is the better value.

To reiterate, in my experience no one should operate an evaporative humidifier for any length of time without a bacteriostat. Doing so can pose a health hazard, especially for those who already have a respiratory problem.