|Reverse Osmosis filters makes water acrid. Plastic tubing is needed for RO water. It eats copper.
Corrosion has been major problem with steam humidifiers. The manufacturers blame chlorine and include a charcoal filter. The charcoal filter needs to be replaced once a year to be effective in removing chlorine. Never the less we hear from customers with heating elements showing premature corrosion. On the top left photo is a Honeywell HE440 that was in service for a week.
The Skuttle and White-Rodgers steam humidifiers have been in service for decades. A few years ago they upgraded the heating element. The element is now larger and surrounds the float. The float was plastic but now it is stainless steel. We stock only the new models. Premature corrosion is NOT covered under warranty.
Filters such as reverse osmosis can leave water acrid as shown on the bottom left photo. Acrid water can be balance by calcium treatment, a filter that slowly dissolves calcium in to the water. For steam humidifiers we recommend a expert experienced with your local water to help determine a series of filters and treatment that will balance your water.