Distilled water is water that has been filter (all the minerals have and other impurities have been removed.) Its been heated so all micro organisms contained in it are also removed. It is in essence, pure water and nothing else. Its pH is often neutral 7.0 . . . Distilled is good as using it often will not cause a pH imbalance (depending on the strain, some like levels around 6, other like it higher like 6.8. Tap water can be good or it can bad, it depends on where it comes from. For example, where I live is unique from most places in the world, the aquaphers run through a bedrock of limestone. The pH of my tap has a pH higher than 8.0 (I'm not sure how high goes cause thats as high as my scale goes to judge it lol). Its the reason why I dont need cal mag for my plants: my plants get all the calcuim (limestone) they need. I do have to add espom salt (magnesuim) once in the end of veg and again two weeks before the end of flowering.
You can use tap water, it can be good for your plants. But if you so, make sure to remove the chlorine and know whats elements are contained in it, and add those that are missing and dont add more elements that it already has in aboundance. Lock occurs from difficentcies or overdosed alike.
Most nutrients have micronutrients in it, so most of the time you dont have to worry to much about adding anything. The two MAJOR micronutes should be of concern: cal and mag. The plant uses this in somewhat abundance at certain times of its life cycle.
Howie, where you live has a basilic bedrock, so if you use tap water make sure you have a bag of cal/mag, as your tap wont have much cal in it. It wont hurt your plants so long as it sits the chlorine has evaporated (24hrs or so).
How much money do you spend on water a month for your thirty plants? Time that times twelve, and thats how much money you will save in your small business annualy.