My lather went flat during a hot towel shave and it was a mess

I had a client come in for a hot towel shave earlier, and everything was going fine until I applied the lather. The soap seemed to mix well at first, but after putting it on his face, it just lost all its thickness and slid right off. I tried to brush it back on, but it kept getting watery and wouldn't stick. The client started fidgeting because the lather was dripping, and I had to hurry through the shave. It left his skin irritated and I felt really embarrassed about the whole thing. I'm guessing my water might be too soft or the soap ratio is off. What's your go-to method for checking lather quality before a shave? Do you adjust based on water type?