Here's an indispensable resource for anyone wandering around London on a hot summer's day. Find a Fountain maps hundreds of drinking fountains, both working and long dry. The map is UK-wide (with a few entries in other countries), but there's a particular focus on London.
The site was originally launched by Aquatina, who make reusable and collapsable drinking bottles so you don't have to keep buying bottled water. It's now ran in association with the 1859 Drinking Fountain Association charity.
The site encourages users to upload details of fountains that have so-far escaped notice. We've already spotted two omissions, oft-used by a wandering Londonist: the British Museum's basement refreshment points, and the welcome upright fountain in the middle of Hampstead Heath. Please do go and share your own aqueous knowledge.
And, remember, if you over-fill your bladder with free water, there's always Ian's map of public toilets to offer relief.