Micro-organisms were unknown until the invention of microscopes AFAIK, which was in the 1600s AD. People thought diseases were caused by imbalances of the elements, miasma, possession by spirits, etc. in ancient times because they didn’t know about the micro-organisms that cause illnesses.
It is distressing to find visible living beings (mosquito larvea) in your water supply. I had this problem for 3 months at my kuti. They would come rushing out the tap in quite a shock that they had been brought into daylight. It turned washing my alms bowl into a 40 minute endeavour while I filtered and rinsed and peered.
No there are not. (Someone please correct me if there are.) Those days it would have been a simple cloth filter. Remember this is for filtering visible organisms. I would assume that it was understood that you would simply rinse the cloth when you were done simply as a matter of keeping things clean.
“If anyone were to say that just as a person does a deed, so is his experience is determined by it, and if this were true, then living the holy life would not be possible, there would be no opportunity for the overcoming of suffering. But if anyone were to say that a person does a deed that is to be experienced, so does he experience it, then living the holy life would be possible, there would be an opportunity for the ending of suffering. For instance, a small evil deed done by one person may be experienced here in this life or perhaps not at all. Now, what sort of person commits a small evil that takes him to hell? Take a person who is careless in the development of body, speech and mind. He has not developed wisdom, he is insignificant, he has not developed himself, his life is restricted, and he is miserable. Even a small evil deed may bring such a person to hell. Now, take the person who is careful in development of body, speech and mind, He has developed wisdom, he is not insignificant, he has developed himself, his life is unrestricted and he is immeasurable. For such a person, a small evil deed may be experienced here or perhaps not at all. Suppose someone throws a grain of salt into a little cup of water. That water would be undrinkable. And why? Because the amount of water is small. Now, suppose throws a grain salt in River Ganges. That water would not be undrinkable. And why? Because the amount of water is great”