I purchased a WaterBoss ProSeries water softener and plan to install it immediately before my water heater as described in this post.

The instructions for the water softener indicate that 3/4" pipe must be used between the water softener and the water heater. However, the existing pipe supplying the water heater (shown in blue) is 1/2".

Is there any reason I would need to step up to 3/4" between the softener and the heater?

I can't think of a reason, but I'm also a novice whose confidence is his weakness.

Water Softener Plan

P.S. Bonus points if you read that last bit in Emperor Palpatine's voice.

  • 1
    The flow rate is the difference. 3/4's flow rate is about double that of 1/2". I'm no expert but it seems like that 1/2 could create a bottleneck if too many water outlets are bring used at once.
    – Tyson
    Oct 13, 2016 at 13:56
  • are you saying that the city supply line is 1/2 inch?
    – Alaska Man
    Oct 13, 2016 at 19:42
  • @alaska man the line going directly into the water heater is 1/2 inch.
    – T.D. Smith
    Oct 13, 2016 at 20:42
  • Yes I understood that the line going into your water heater was half-inch my question is is the city water supply line half-inch or three-quarter and then steps to half-inch after it enters the house. The norm for city water supply has three-quarter inch. Is all the plumbing after your water heater half-inch. Again the norm that I am used to is three-quarter inch into the water heater three-quarter inch out of the water heater and half-inch branches out to each access fixture. half-inch going into your water heater and then steping back up to three-quarter , pressure will suffer.
    – Alaska Man
    Oct 13, 2016 at 22:08

3 Answers 3


Provided the line coming into your house from the city main is 3/4" and inside your house the line changes to 1/2" there would be a significant increase in flow rate and possible pressure when water demand is higher in your house.

Run a new 3/4" line to the softener as described. They could require the extra flow rate when it regenerates (which could use ~25 gallons/~0.11 m3) when it does this.


You should use 3/4" pipe. Pex is cheap and incredibly easy to install. Just take an afternoon and install the correct piping. Also I agree with others that the city water line coming into the house and to the hot water heater should be 3/4" pipe.


Your city inspectors may require you to "follow the installation instructions." Otherwise the only advantage to using 3/4" pipe from the unit to the 1/2" supply is the slight reduction in possible "water hammer" when demand fluctuates. So if permitted by the inspectors (or if you are doing without inspections/permit) go ahead and use the smaller pipe.

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