Why does she hand me a lime every Saturday?

I asked a woman at a street stall in Phra Khanong for water. She gave me a glass, watched me drink it, refilled it without a word, then handed me a lime and pointed at a bench. We sat for an hour without one shared word. I come every Saturday now with a bag of tangerines. She hands me a lime. We nod. Last week she added a small chair for my bag, which is the biggest thing anyone has ever said to me. I still do not know what the lime is for. I keep the limes.