“I was surprised to read posts complaining about the Wool Fat soap being hard to lather - my boar brush and a little warm water whips up a pile of creamy lather in a few seconds (this town has great water) ... I'm still experimenting with how much water I can add in before it falls apart.“
Yup, it’s all about your water, but could be a brush that needs cleaning.
If you think your water may be an issue, try making lather with a bottle of water.
Clean your brush, soaking in a cup of warm water with an ounce of vinegar for 15-20 minutes and give it a wash with a dollop of shampoo in your palm. It will also bloom your brush nicely.
If you have hard water, a drop or two of glycerin will help with your lather. Soaking and shampooing your brush will make a big difference.