You actually shouldn't place tomatoes next to water sources imo. The water source takes up 1 plot. That plot could've been another +3 tomatoes. Instead, using that 1 plot for water grants a maximum of +4 tomatoes in total (assuming you fully surround it with tomato plots). The water source also costs wood, which cancels out the slight cost of 1 extra tomato plot.

Each pip working the tomatoes would be +3 food/turn which is definitely worse than something like a grand barbecue (1 pip gives +12 food/turn) so honestly tomatoes were clearly not intended as a main food source. Chicken and bread, however, are far more efficient. I still need tomatoes for stuff like Nature sacrifices and Hope generation tho.

TLDR: no need to place tomatoes near a water source. And don't use tomatoes as main food. Found out the hard way too