Whoa. That is really bad advice.
First of all, you are dead wrong in saying "flowers and veggies grow all over the world and lots of nasty and good water comes out of hoses to water them and they all produce food or flowers". That is just completely false. They don't all produce food or flowers. People fail to produce flowers or the flowers shrivel prematurely due to having too high of pH coming from the hose (hydrangeas are a great example). People lose plants to contamination a lot. Plenty of studies have also shown that plants uptake a lot of heavy metals from contaminated water, which can be passed on to us. People also lose plants to bad pH a lot. It's one reason you don't find tons of people planting blueberries in Indiana (where I am). Unless you amend the soil heavily, the pH is too high for them and they will either produce very low yields or die. You can grow them, but only when you are smart enough to take pH seriously. Otherwise you will fail miserably.
Second, if you wait until your plant is exhibiting visible signs of pH problems then you waited way too long. It doesn't happen overnight. It can take a week for plants to start showing the signs to you. That is a week of damage. Then you have at least another week of fixing the damage if you can even do so. The vegetation in place that has been damaged may not recover, so you will have to wait for new if that is the case. Just depends on the damage. You could lose fruit and have to start all over with fruiting. The fruit that is present, if not lost, will have suffered
nutrient deficiency, too. What is the point of growing your own food if you aren't going to make it as nutritious as possible? Why risk losing precious weeks? If you grow outdoors, you have limited time, anyway. Doesn't seem worth losing that time over ignorance of a very important factor. One unbelievable common example is BER of tomatoes. If you let your pH get out of hand and allow the
nutrients to precipitate, you can lose every single tomato on the vine. BER is one of the most common problems in hydro tomatoes. Why increase your chances
Third, I spend enough on nutrients. Why would you want to waste them on ignorance of the importance of pH? pH swings can cause your nutes to precipitate, as I mentioned. That makes them useless. Need evidence? What's that rust color on the inside of your rez when you let it get to pH 8 for a long period? It's the iron that fell out because iron disagrees concerning the importance of pH. And that's just a highly visible example.