Some runners throw the trash in its right place, some don't. We need not worry as good race organizers clean up after themselves, anyway. However, we as people who joined the race still created waste and made use of hundreds of trees when we could have saved some of them by the simple act of bringing your own water bottle.
Everyone brought their own water bottle at the Sole Racing event last April 21
Think. When you ran 21k, you would have made 5-20 stops to hydrate yourself. Assuming you used a cup per stop, you had used 20 cups, multiply that with the number of participants. If you brought your own water bottle, you would have eliminated the need to use 20 cups and you wouldn't have contributed to the waste.
In the bigger picture, you had saved a few trees that will be cut down to create more plastic cups. You will also save space that 20 cups of waste could have used.
One more thing, the race route will be better to look at.
With the right hydration belt, you could run without carrying a bottle.
On your next race, BRING YOUR OWN WATER BOTTLE.