Thirsty Londoners will be able to get free water from 20 new fountains and an array of businesses participating in a new scheme.
The fountains will be installed in the summer, across London, along busy commuter and shopping routes such as Oxford Street.
Businesses in five areas "with lots of food outlets" will take part in a bottle-refill initiative from February.
The plans are part of a £750,000 scheme to cut plastic waste.
The money will be spent over three years, according to the Mayor of London Sadiq Khan's new draft budget, and is part of the mayor's ambition to send no biodegradable or recyclable waste to landfill by 2026.
Exactly which businesses will take part in the initiative are still being finalised, but the mayor's policy team is looking for busy areas where water can be offered to people easily, a spokeswoman said.
The participating areas will be announced in February and the scheme will run until the summer initially, before being rolled out across the capital if successful.
Most of the £750,000 budget is expected to be spent on installing the fountains and helping businesses to promote their participation in the refill scheme.
Eventually Mr Khan wants to see more fountains, City Hall has said, while adding that he did not have an exact number in mind.
Mr Khan will answer questions on his draft budget during a London Assembly hearing on Thursday 25 January.
The mayor's draft London Plan urges local authorities in the capital to identify "appropriate locations" for free water fountains during the planning process.
Network Rail said it was "supportive" of having water fountains in its managed stations.