Couldn't Risk It

I decided to try a smaller restaurant with just one local eating at one of the four tables. The vegetables on rice was really tastey, I enjoyed every mouthful until she brought over my glass of water. It was yellow. Almost the colour of apple juice, I'm not kidding. I decided to keep smiling, not drink the water, and believe if my food was made of that water, at least it's cooked. The other guy was eating what I had and he seemed fine. Then he asked how much Thai I knew. After I listed all 3 of my words, we all laughed and had a good broken conversation. He works security at the airport. She asked if I travel alone. Instead of the surprised looks I got in Malaysia, here I get thumbs up and "that's good!" responses. It was all fun until she came over and asked if I was going to drink my water. How do you indicate nicely that you don't want to drink yellow water? Automatically she turned away looking upset and pretended to be busy. I thanked her for the delicious food and she politely smiled, but I felt so bad... :( P