Distilled , spring , and tap water are all very different from one another . Distilled water is heated to a steam and then recollected , this removes all impurities and minerals from the water. Spring water is filtered over rocks naturally , and is full of minerals . Tap water can very greatly depending on the type of treatment it receives , where it is drawn from , and how its filtered. Most city municipals add chlorine and other chems to the water , also it is usually highly filtered . The city may also choose to Ion exchange the water or even do reverse osmosis before allowing it to be consumed. I would expect that spring water would have a higher ppm somewhere between 200-400ppm , while distilled will have a very low ppm compared to tap water. Distilled water should be 0-10 ppm Tap water can have a range of 50 - 250ppm depending on the treatment. This is why a lot of pple choose distilled water over spring or tap water. With distilled water you start from a very low ppm , adding only what you want the water to have you have a better knowledge of what exactly is making up your TDS.