Kosher Water: Filters

https://a.co/d/h8tWXqU I wanna know if this filter is good for under the sink to protect from warm

Shalom!

Thank you for your question.

The need for a filter on your local water supply will depend on the quality of the tap water where you live.

As a general rule, something that cannot be seen with the naked eye, is dismissed and ignored from the perspective of Jewish law.

For example, a blemish on an etrog will only disqualify the etrog if it can be seen with the naked eye. If a magnifying glass or microscope is required to see the blemish then it is ignored and the etrog is kosher. Similarly, the Torah tells us that in order for a fish to be kosher it must have both fins and scales. There are some fish that have scales, but the scales can only be seen under a microscope. Such fish are considered to be non-kosher since the scales cannot be seen with the naked eye.

This brings us to your question on drinking the local tap water. If one were to take a microscope to the water supply in most cities, one will find organisms floating in the water. One may drink such water since the organisms cannot be seen with the naked eye. In fact, there are living organisms in the air we breathe that we “consume” without even knowing.

If you do not see any organisms in your water then you can drink the water without worry. Nevertheless, filtering tap water is always a commendable route for both halachic and sanitary considerations. It appears from the description of the filter that you sent us for review that this filter ensures that nothing visible to the naked eye can enter your water.

See Aruch Hashulchan, YD 84:36.