Hello
I have been told that water hammer is due to high pressure of my incoming water so can I reduce the amount of water pressure from my mains by simply only turning it on to half pressure,

No, you will reduce volume and not pressure. Is your system equipped with a Pressure Reducing Valve? If not you should install one and limit the inside pressure to no more than 50#.

Water hammers main cause is when an automatic solenoid opens or closes. In example dishwashers clothes washing machines and sometimes humidifiers. The only remedy is installing hammer arrestors. Home Depot sells a hose thread style that attach to the connection for CWM. Not sure how the work considering they are not installed on the riser per code. Closing your main valve will not reduce pressure in a closed system.
Mac

Some plumbers put a capped riser above shut off valves to hold air. These fill up with water over time. Drain and refill the system to fill with air is you may have these(usually inside wall)
Mac

Hi BradleyJ

Pick up a "hose-bib" pressure gauge (see images) at a local home improvement store and attach it to an outside faucet and then turn the faucet on...what does the gauge read? If the pressure exceeds 80 P.S.I. then all plumbing codes require that a PRESSURE REDUCING VALVE (PRV...see image) be installed and pressure be dialed back to somewhere around 50-65 P.S.I. If you have a PRV then you should be able to reduce the pressure by turning the bolt on top...dial in desired pressure using the bolt on top of the PRV and the gauge at the outside faucet, right?

If your pressure reads at less than 80 P.S.I., then you probably need to install water hammer arrestors or strap the pipes better as mentioned above...;)

Back to you...

Mark

Not all codes. This here Detroit water! At least we got that Going for us haha. Rare if you're under 100 psi around here. No PRVs. Keeps us busy rebuilding though.
Mac

Keeps us busy rebuilding though I don't doubt that for a second!

What code do you fall under, Mac?

Michigan plumbing code. 80+ actually does require it. Just not enforced.
Mac

Yeah, I was pretty sure all codes required it in USA...;)

Thanks!

I have been told that water hammer is due to high pressure You were told wrong. While excessive PSI can contribute it's not the main cause, The main cause is a lack of air chambers or air chambers that have loaded up wit water and need to be refreshed.
One of the "Water hammer" happens when you abruptly shut off the water. You have at least 40 pounds of pressure pushing the water flow. The weight of the water hitting a 90 degree bend causes the sound that you hear. We put in air chambers to cushion the hammer much like the shocks on your car.
Back in the 60's we were required to to put air chambers on all bath lavatories and kitchen sinks. Over time water and condensate built up in them and they must be recharged. First turn off the house at the main house shut off valve. Then open hot and cold faucets at the farthest bathroom to prevent air lock.(This is important.) You will find under each fixture little brass or chrome valves. These are called angle stops. With a small pail held under the angle stop to catch the run off look under the handle of the stop and you will see a nut with the stem running through it. This is called the bonnet packing nut. Put your wrench on it and back it off counterclockwise. Now open the stop and remove the stem and washer assembly, The stop will began to drain. When it has quit draining reassemble the stop and move on to the next one. Do this on each one of your angle stops. There will be six of them in a two bath home. When you are done, close off the faucets you have opened, turn on the water to the house, and give yourself a pat on the back.
You have just recharged your air chambers and saved yourself a hefty service call bill. Hope this helps you out and thank you for rating my reply. TOM