Ducklings grow quickly. Our runners doubled in size their first week. I am not exaggerating. So plan for Brooder II now - I went to Brooder III - we had eleven ducklings!
Here are some ideas for water management
https://www.backyardchickens.com/t/641902/created-a-water-saver-for-my-duck-brooder
https://www.backyardchickens.com/t/679433/water-water-everywhere/10
https://www.backyardchickens.com/t/858161/feed-water-solution-for-brooder#post_12901321
http://frankiemakes.blogspot.ca/2012/06/watering-solution-for-ducks.html
https://www.backyardchickens.com/t/259876/do-your-ducks-have-water-at-night/10#post_13568197
Here are some ideas for water management
https://www.backyardchickens.com/t/641902/created-a-water-saver-for-my-duck-brooder
https://www.backyardchickens.com/t/679433/water-water-everywhere/10
https://www.backyardchickens.com/t/858161/feed-water-solution-for-brooder#post_12901321
http://frankiemakes.blogspot.ca/2012/06/watering-solution-for-ducks.html
https://www.backyardchickens.com/t/259876/do-your-ducks-have-water-at-night/10#post_13568197