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Question DetailsAsked on 3/14/2015

when i flush my toilet downstairs i lose almost all water my shower upstairs. why?

i have a well and recently moved into this house. when the toilet is flushed the shower almost stops completely i have changed the water filter and no fix.

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1 Answer


Several possible causes for this:

1) your pump capacity or pressure is low, so it just cannot serve multiple high-demand uses at the same time. Could be due to small pump size, undersized piping, pressure switch on pump set too low, plugged sand filter, plugged or corroded well screen, or several other causes. If this is the case, same thing would happen if another shower/tub or the washing machine was turned on while showering, and possibly when dishwasher is filling too.

2) pipes are partly blocked with iron or lime or manganese buildup, so they just cannot deliver the needed water flow

3) you have a flow restriction in the system such as a pressure regulator or undersized piping that is inhibiting flow


A shower takes up to about 5-1/2 gpm (gallons per minute) with an old (pre-about 1992) shower head without a flow restrictor disc, or about 2.2-2.5 gpm with normal one built after then, or about 0.75-1.5 gpm with a low-flow shower head. A normal faucet produces about the same amount of flow, again depending on year of manufacture and whether low-flow or not. A toilet refilling can run from about 3-5 gpm for modern ones, to as much as 10 gpm with older 5 gallon flush ones.

So you can see, if your pump cannot produce about 7-15 gpm total at the house, using two high-demand devices at the same time can result in a dramatic pressure drop.

I started writing instructions for assessing this yourself - but the instructions would be just too long. Google for articles on testing household water pressure and flow, or call a Plumber.

Basically, if about the same drop in water flow occurs if you are running the shower and then turn on an outside fauceet all the way (without a hose on it), flush any toilet, or start the washing machine filling, then it is highly likely that the incoming flow capacity is too lowfor the amount of water you are using - due to partially plugged pipes (especially if steel), undersized piping, low pump capacity, or low well inflow capacity.

You can get a ballpark idea by measuring how many seconds it takes to fill a bucket or large can at the first faucet on the house side of the pump (usually a drain valve right after the pump) and compare that to how long it takes to fill the same containar at an outdoor faucet or interior drain faucet on the house - should not take more than about 1/4 longer to fill at the house (due to the longer pipe run resulting in more flow friction), and at shower (if you have a tub faucet there) should take about same time as at the outdoor house faucet. Also - check what flow you are getting in gpm at the faucet near the pump versus the nameplate on the pump - that should give an idea of whether you are getting anywhere near the rated capacity from the pump. Of course, distance from the pump, number of pipe bends, shutoff pressure on the pump, etc all affect the flow rate actually available at the house.

If you think the issue is internal to the house, Plumber is the one to call. If you think it is pump capacity or possibly undersized piping from the pump or pump pressure too low, then a Wells and Pumps company is the one to talk to.

Another possible fix is to restrict flow rate at the valves on the toilets, so the inflow rate is restricted - so toilets take far longer to fill, reducing the effect on the shower. That might be your first try - to solve the problem by restricting the flow of water to the toilets, assuming flow for toehr purposes is adequate. Called toilet flow restrictors - many different types, not tough to install yourself in many cases. Some go at the shutoff valve where the flex tubing threads onto it, some at the tube to toilet connection, some in the toilet float/filll valve itself. Can make the refill a bit noisier - you are likely to hear a louder sound of water running when toilet is refilling. Cost from just a few bucks for the disc or helix type that go in the end of the flex tubing or bottom end of the fill valve, to more like $10-25 for the variable-flow valves that go in-line and allow you to vary the flow rate. Available at home improvement stores and box stores and many places online.

Answered 5 years ago by LCD

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