Removing the bumper 15 minutes makes cleaning and inspecting the washer bottle easy, as above most likely the little black filter in the bottom of the bottle is clogged up with slime.
Once you have the bottle exposed you can remove the pump.
1
Do this by pulling it upwards, expect quite a lot of water flow.
2
2a
Then remove the little black filter, and wash it under the hot tap in the sink.
3
Washing it will clean out the perforated holes of the filter.
3
Wash the bottle out as above with diluted bleach water, swill it out at least 4 times after cleaning, then then refit the filter and pump, top up the bottle that is the bottle sorted out.
It could be the T piece where the two washer jets join under the bonnet cover.