Your water barrel fills with .5 water.

Fluid barrel mod adds a water barrel that fills and empties 25.

With your mod installed it fills a barrel for .5 and the empty recipe remains for 25.

I would probably add an optional dependency for this mod on fluid barrel -- then you will load after it.

dependency example:
"dependencies": ["base >= 0.13.0", "? fluid-barrel >= 1.1.1"]

And then chick if water barrel exists before adding your version check for it:
if data.raw.recipe["fill-water-barrel"] == nil then
data:extend({ {
type = "recipe",
name = "fill-water-barrel",
category = "crafting-with-fluid",
energy_required = 1,
subgroup = "barrel",
order = "b",
enabled = "false",
icon = "homeworld/graphics/icons/fluid/fill-water-barrel.png",
ingredients =
{
{type="fluid", name="water", amount=0.5},
{type="item", name="empty-barrel", amount=1},
},
results=
{
{type="item", name="water-barrel", amount=1}
}
},})
end