On a boat, the water pressure is managed by a pump located in the bilge, which is activated regularly to restore pressure in the pipes. When you notice a drop in pressure (in the shower or the kitchen), leave the faucet on and the pump will eventually activate.
In the kitchen, an under-sink filter is installed as a precaution to ensure that all impurities in the water tank are filtered out. Even if the water in the tank is entirely drinkable, we recommend that you fill your water bottles in the kitchen.
For the same reason, you will find that the pressure can be reduced a little (or even a lot) when there is not enough pressure in the pipes. In this case, let the water run and at some point you should hear the pressure pump activate and gradually the flow will improve.
Warning: This can also have an impact on the temperature of the water when you do the dishes, so be careful not to burn yourself!