190 Ppm Tap Water Spike?

I've been using my tap water for months at 290 ppm, yesterday I realized my ppms were really high for the amt of nutes I used, I poured some nutes out, replaced it with some tap (all my tap water sits out for at least 24 hours) and it was still really high. Today the same thing happened I was like wtf and checked my plain tap water.. 480PPM!! What could cause a 190 ppm spike like that? I'm gonna have to dilute it with distilled.

Rain, city flushing or something of the sort... check it in a few days and it will probably go down

That makes sense, I've heard of rain spiking it but it hasn't rained recently. 480 is really high