I will tell you a little secret, water is certainly not all that will control the thickness of lotions which is why I advise doing little batches and lots of testing. Types of emulsifiers and thickeners play a huge difference. One day I decided I wanted to make it really thick like cream by just cutting the water down to around 65% using the normal recipe I had been making and selling for years which had a water usage rate of 74.5%. Guess what, the stupid 2 gallons decided to separate shortly after bringing it to emulsion and it started to cool down. After mulling over for a little while how to fix it, I reheated my leftover water which had already been heated and held, measured out an additional 10%, and started mixing it in increments waiting to see if the emulsion would go back together and hold. Thankfully it did and I had a couple of weeks before my show so I had time to bottle so I was able to let it sit and determine if it would hold.
The point of the above explanation is I have made creams with 65% water using Ewax with no issues, but my formula that separated it uses Polawax. I have also made very thick lotions with 86% water just using different emulsifiers such as NCD-20 and Glyceral Stearate, so there is just no easy answer. I am sorry, leave it to me to complicate the issue, but with lotions, I never found just one answer. Not being a cosmetic chemist or any chemist for that matter, I had to experiment and test test test, which fortunately I enjoyed when it came to lotion making.
@AliOop, I found my lotion notes on my computer!! It was Arnica-infused lotion that grew bacteria and mold, but I see it was before I was using my 2-system preservative and used Germall Plus as the preservative. When I get relocated I just might re-address this so Autumn will have something new to put under her microscopes.
Our recipe is loosely based on this one, but this is the recipe my daughter originally learned to make lotions with and Swift Crafty Monkey site. The kit is no longer available and I do not agree with Ann Marie's lotion-making methods, but the recipe is nice and stable. One of WSP's emulsifiers is the same or similar to Polawax, just check the ingredients.
Make Lotion from Scratch on Soap Queen TV - Soap Queen
@LynetteO I just made my own base un-fragranced and stored it in new HDPE buckets which you can buy from paint stores, so I always had lotion ready to go.