Leach and leech are easily confused words. The spell-check application of most word processing software programs would not catch a slip-up of these two words. Spell-check is looking for words that aren’t in its dictionary, and words that resemble words in its dictionary but are possibly spelled wrong. Spell-check isn’t perfect. It doesn’t know and can’t guess what word you wanted or what word you meant, it can only judge the words on the page. If you used words that are all spelled correctly, it gives you a pass anyway. Similarly, autocorrect on mobile phones might suggest one word instead of the other, it would be easy to do since both words start with “l-e.”
Leach is a verb. It means to remove a substance by percolating it through water or another liquid. It can also describe chemicals releasing decomposing trash into surrounding dirt and and water supplies, or chemicals in metal or plastic containers altering the items stored in those containers. In recent times, there’s been concern that BPA from canned or stored food has leached into food and drinking water products.
Leech is a noun. It means a dark-colored flatworm that feeds by suctioning blood from the skin of other creatures. Leeches live in swampy areas and brackish waters.
It can also describe someone taking money or taking credit they didn’t earn or deserve.
The following sentence uses both words correctly:
Len, an avid outdoorsman, was far more nervous about toxins leaching into packed food that encountering leeches while he fished.