It depends on what you meant by saying not visible. Of it is not visible by using accurate measuring equipment then I think so, but if you mean that all transparent water is drinkable, then no. Think about this. When you put salt in water, you can't see it but it is still there: if you taste the water you can tell that there's salt in there. Let's say that instead of salt there are some bacteria, or some other type of salt which is not appropriate to drink at high levels, such as nitrates. I personally wouldn't recommend drinking from any type.of water unless you are not sure about its purity