I know that washing basil weakens it's flavor significantly. I often buy it from local supermarkets where everyone can touch it, that's why I just have to wash it. But even when I buy organic basil, I still feel the urge to wash it. How do you deal with that? Is there any way to 'wash' the basil without weaken it's flavour?
People generally wash fruit and vegetables (organic or not) to remove surface contamination ,and the bacteria it may host, from the farm and supply chain
This includes soil (ground based animal faeces), compost (rotted vegetable matter), airborne dropped bird faeces, road dust (often high in animal faeces), and other surface contamination that can host bacteria
A short and simple wash by hand in a bowl or sink of cold tap water will remove large amounts of these surface contamination from most fruit and vegetables. Some may require light brushing or scrubbing. And for best results rinse in running cold tap water after washing. Shaking water off usually works better than trying to blot it off with a tea towel
Gentle washing will NOT remove any significant flavour or aromas. Think about what happens when it rains :-)
If you feel the urge to wash it before using, then wash it. The stress of not having washed it is not worth it.
I used to work in the Adelaide Central Markets, and having seen what some people did before touching the produce, I habitually wash goods that were within reach of the public before I use them. When you've seen customers stick their hand in their pants to scratch their butt and straight afterwards pick up the fruit, you get a bit paranoid.
I accept that most of the time, I don't need to wash the produce. I also accept that that does not matter to my brain what I tell it, if it wants me to wash the stuff before using it, it's not worth arguing.
When I do wash my ingredients, I don't dry them immediately. Instead, I leave them in the dish drainer on the sink while I do another part of meal preparation. Most of the water will drain away without having to put in any effort, and what's left can be shaken off or blotted, depending on how fragile I feel the ingredients are.
The other way you can deal with feeling the urge to wash produce before using it is to grow your own, or acquire it from a friend or relative. I get my basil from my Dad, who always grows about ten times as much as my parents will use.
Washing basil DOES remove flavour, as the oils accumulate on the surface of the leaves. Unwashed leaves taste like basil, and washed leaves taste like grass clippings (i.e. chlorophyll). This can be confirmed by any Italian nonna, or even just by tasting your basil plants after a good rain (or, before and after a wash); the flavour is noticeably diminished.
You can just use more leaves to compensate for the lost oils with most dishes, but pesto is virtually ruined with anything but unwashed leaves, getting that unmistakable grassy/banana-y/chlorophyllous taste. That said, I defo wash store/market basil regardless; use the coldest water and least agitation reasonably available to you...it's still gonna suck tho.
Of course, the only way you can (relatively) safely omit washing is to grow your own, ideally using an inert growing medium like a peat-based potting mix. A raised bed would give you an extra layer of protection from the feces of ground-dwelling critters like dogs, cats, raccoons, etc.
Washing basil (or indeed, anything) in lukewarm water is going to do very little to remove germs; in fact, you're probably just giving them an excuse to party.
Basil is easy to grow in a pot on a warm windowsill, so perhaps you could grow your own and avoid any misgivings about the hygiene aspects that way?