How to determine Quality
Don't literally buy into the hype on labels. There is no regulation on the Aromatherapy industry, so Essential Oil (EO) companies can legally say anything. Terms like "100% Pure" or "Therapeutic Grade" get thrown around a lot, but do not ensure quality. The only way to guarantee pure, therapeutic grade quality is to do your homework. I strongly encourage you to not only look into a company's product standard practices, but also their ethics and sustainability practices.
The only way to determine the actual quality of an EO is to inquire about it's Gas Chromatography/Mass Spectrometry (GC-MS) testing. This complex, third party testing method is an analytical technique that separates, identifies, and quantifies trace levels of chemical substances. It can prove that there are no pesticides, solvents, or other adulterated compounds in the finished product of a single EO. This information should be completely forthright and easily accessible by any ethical EO company. The FDA does NOT presently regulate EOs, and there is no other government regulatory agency in effect to protect the consumer from poor business practices in this area. Therefore, if you cannot easily find this information through a quick web search or phone call, then I would strongly urge you to avoid working with that company.
A word about Safety
Many people are unaware of the dangers of Essential Oils, and the latest explosion in popularity has uneducated consumers constantly risking their health and safety. For instance, many EOs are contraindicated for pregnancy and breastfeeding, and you should never apply them to children under one year of age. Some EOs are phototoxic- which means they react to the light of the sun and can cause second and even third degree burns. Others should never be used on or even around (i.e. diffused) pets. So you see, it is absolutely imperative to not only know what EOs to use, but also when and how to best utilize them.
Essential oils are highly concentrated plant medicine, and should not be taken lightly. Even if you have no sensitivities to the plant itself, the essence of it's oil could potentially cause a reaction. Not only that, but because they are so highly concentrated, you only need very little. Most importantly, they should very rarely be ingested! Even in the most severe cases, a certified Aromatherapist with an adequate education in the delicate chemistry of Clinical Aromatherapy, would NOT recommend that someone ingest essential oils without first exhausting every other option; And even then, the protocol to consume them would not exceed 6 drops total in one day. They would also be combined with a proper binding agent in order to prevent internal damage.
Although they are considered an oil, the viscosity of essential oils is unlike that of all other vegetable and nut oils. They are not really an oily substance at all, which gives them an advantage of being more easily absorbed through the skin, but also the disadvantage of not being water soluble. This means that when applied neat (undiluted), they are quickly absorbed into the bloodstream. Which is good, but because they can also cause rashes and burns, they need to be properly diluted in a carrier oil that is not as easily absorbed. It also means that when ingested, they will inevitably burn fragile mucous membranes- and by putting drops in your water you are not preventing any of that inevitable damage. Burning the lining of your internal organs is the least of your worries, because essential oils can also cause toxic liver damage if consumed in excess.
So please, if you are unsure of anything, it is safer to err on the side of caution. No disrespect to MLM/Direct Sales companies, but watching a webinar or two does not make you an expert. If you have questions, please consult a qualified professional. (P.S. I happen to be one of those).
A word to the wise....
This is a rare occasion where the term "you get what you pay for" does NOT apply. For instance, paying more for an oil does not guarantee it's purity or quality. I am not denying the quality of some brands, but I will guarantee that you will pay significantly more for the same quality of oil that you buy from an MLM/Direct Sales brand that you would anywhere else, simply because of the Network Marketing design. I have nothing against Network Marketing, and there may even be some great incentives to join, but as a Professional Aromatherapist (who uses essential oils daily in their Clinic) that is not cost effective for me. So if you are like me and use essential oils regularly, then you may want to consider shopping small. One really good resource to find more information as well as trusted Aromatherapy brands, is through the National Association of Holistic Aromatherapy.
Quality Essential Oil brands that I personally trust:
Other Reputable Companies that I have not personally used: