pH doesn't test how much of something is in the water but rather the relative acidity / alkalinity of the water. Distilled water has no acids or bases in the water so it has little effect on pH.
We use dilution for testing pH because high chlorine causes the pH test to read falsely high.
The limit for the Taylor pH test is 10ppm chlorine. In your water, I'd dilute 2 parts distilled to 1 part pool water, test that mix and call it a fair approximation of your pool's pH.