I have a bunch of pumps but the water is in low pressure. Is it a bug?
Factorio's fluid simulation is rather quirky and you should not take the numbers on pipes too seriously. (It currently simulates equalizing amount of fluid in adjacent containers, like water sloshing in an open tank, not realistic pressure/velocity. The number you are looking at is the amount of fluid.) Look at how much production you're getting from the machines on the other end, not the exact number. That said, there's some definite room for improvement in your picture:
You have too many offshore pumps per pipe, so you aren't getting the most output from your pumps because it's limited by the pipe maximum flow rate. If I remember correctly, the ratio is about one offshore pump per pipe, but you can get a little bit more by using two per pipe (wasting most of the capacity of the second pump, but maximizing the flow in the pipe).
Run multiple pipelines in parallel from pumps to consumers.
- Avoid creating any junctions, except to supply multiple consumers from one pump or to connect two pumps to one pipeline. If you run pipes adjacent to each other, use underground pipes to avoid them connecting. (Such unnecessary paths can reduce flow in other directions.)
For long runs, use underground pipes whenever possible. The reduction in flow depends on the number of pipe segments, and underground pipes count as 2 segments no matter how much distance they span.
Here's an example of some pumps I built:
This information is current as of Factorio 0.16.51. A new fluid system is planned for version 0.17, though that is of course still in development.
The technical implementation details of Factorio's pipe system still have some room for improvement. The Factorio devs plan some refactoring for the upcoming version 0.17.
Until then it is advisable to not use more than one pump per water network. One pump can supply up to 20 boilers. When you need more pumps, give each pump an own pipe network which connects it to its water consumers and is not connected to the pipes supplied by another pump.