You ALWAYS add caustic to water, NEVER the other way round. Sorry to shout but this is very important.
Caustic burns are worse in many ways than acid burns. Can we have eye protection and gloves please.
And use cold water; adding the caustic granules causes the solution to warm up anyway. If you add it to already warm or hot water and get localised boiling it will spit everywhere.
The voice of experience, this is. I was inspecting some equipment in a milk processing plant some years ago and the stainless steel pipelines had just been hot caustic cleaned. One of the pipe unions wasn't tight, and about a teaspoon of caustic liquid sploshed onto my head. I wasn't wearing a plastic helmet as it wasn't that kind of risk zone.
I knew instinctively what had happened, even before the hurt started, and I ran to the nearest fire bucket and plunged my head into the water.
The next day a chunk of hair about the size of a 2 inch paint brush fell out.
Caustic soda is stuff to treat with a lot of caution and respect.