Gravity fed water pressure varies depending on several factors. The location of the water tank, the size of the pipe, devices installed on the water line, and the path of the pipeline all determine water pressure. The key is to choose the variable to adjust that costs the least to manipulate. Every waterline is installed differently and has different features. Start with the simplest fixes and continue to make bigger, more costly, changes until you have the water pressure required.
Add manometers. Pressure gauges placed in different locations on the waterline help pinpoint the water pressure problem. Ideal locations for manometers include the lowest point on the line, where the pressure should be highest, at the end of a valley or flat section in the pipe, and at the top of any section where the pressure was forced to push the water up a line. The water pressure should be weak here. Once you know where your high and low pressure points are, you can begin making modifications.
Change the valves, faucets heads and filters. Whether your line feeds a domestic waterline or an irrigation line, if the pressure in the line is high, the problem is with your fittings. Sprinkler heads and domestic faucets, for example, are designed for specific amounts of pressure. If the line is tapped with fittings that can not put out the same amount of pressure the line feeds into them, changing the fittings increases the water pressure. Replacing globe valves with ball valves can increase pressure. Cleaning or replacing filter may also increase water pressure.
Elevate the water tank feeding the waterline. The higher the tank is in relation to the end of the line, the more pressure the line carries. Moving the water tank is costly and time consuming, but adding elevation between the tank and the end of the line generates the greatest increase in water pressure.
Add a water pressure booster. A water pressure booster is an option for homes with good pressure in some locations, but the pressure tails off toward the end of the line. Good locations for a booster are after a valley or flat spot in the line, or prior to a section of line that climbs rather than falls.
Increase the size of the pipe. The more volume a pipe can carry, the higher the water pressure. This is a costly fix because it means virtually replacing the entire system. However, if no other repair can fix the low water pressure problem, it may be your the solution.