Pressure and flow
Weak water at the top of the stair
Low water pressure in a top-floor flat usually comes from old, narrow or shared internal plumbing rather than the mains, says Scottish Water, so first check your stop valve is fully open.
By the Pipes Up the Stair site team · how pages are checked · Updated
A shower that dribbles on the top floor while the ground floor is fine has a few usual suspects. Scottish Water's pressure factsheet, dated 2021, explains most of it: height, timing and old pipes.
Some of the causes are yours to check in a minute. Others need the owners on the stair to act together.
What pressure should you expect?
Scottish Water aims for at least 1.0 bar where your supply connects. Its factsheet says it aims to provide at least 1.0 bar of pressure at the point of connection or stopcock, which should fill a 1-litre bottle from the cold kitchen tap in about 7 seconds. That is measured at the stopcock, not at a shower on the top floor.
Why does height make a difference?
Because water has to be pushed uphill. Scottish Water explains that one bar is the force needed to raise water through pipes to a height of 10 metres, and that pressure depends on your height compared with the reservoir. Every floor of a tenement uses up some of what arrives at the stopcock before the water reaches the top flat.
Why is it worse at certain times of day?
Because everyone is using water at once. Scottish Water says mornings and early evening are the busiest times, so pressure dips then. In a shared stair, a neighbour's shower or washing machine on the same supply pipe can make the difference too.
Why do old flats have weaker flow?
Old plumbing is the usual reason. Scottish Water says low pressure or flow problems in flats are usually due to old internal plumbing that was not designed for modern appliances. In older properties, a single 12.5 mm pipe often fed a whole terrace or group of houses, while modern homes and flats usually get 25 mm.
- 12.5 mmOlder homes, shared
- 25 mmModern homes and flats
Many older flats also have an indirect system. Scottish Water says that before 1989 the most common set-up was a mains-fed cold tap at the kitchen sink, with a cistern in the roof space feeding the other taps. If the kitchen tap is strong and the bathroom weak, that is often why.
What can you check yourself?
Start with the stop valve. Scottish Water says to confirm your internal stop valve is fully open; open means turned fully anticlockwise, and the valve normally lives under the kitchen sink. See finding your stopcock if you're not sure where it is.
If the flow dropped to a trickle just after work on the supply, its supply FAQs blame a pocket of air or a bit of sediment caught in the stop valve. Open and close the valve; if the problem persists, contact Scottish Water.
What are the longer-term fixes?
Scottish Water lists four. For a small or shared supply pipe, the owners on it can install a storage cistern to give a constant supply, relay the supply pipe in a larger size, take a new separate connection, or replace lead pipework. Scottish Water says a home built before 1970 has a higher chance of lead pipework, so in an old stair one replacement can fix pressure and lead at once; see lead pipes in Edinburgh.
Who pays for a bigger pipe?
The owners it serves. Scottish Water says responsibility for low pressure in flats may be shared among the owners. A supply pipe serving two or more flats is common property under the 2004 Tenements Act, section 3, so relaying it is a decision for the stair. For help organising it, the council's shared repairs team offers advice at no charge. Tenants should raise weak water with their landlord or letting agent.
Asked on the stair
Does the ground-floor flat get more pressure than the top?
Usually, because Scottish Water says pressure depends on height and one bar lifts water about 10 metres. The higher the tap, the less is left.
Can the shower pressure differ from the kitchen tap?
Yes, in an indirect system the kitchen tap comes straight off the mains while other taps are fed from a cistern, which Scottish Water says was common before 1989.
Is there a minimum pressure Scottish Water must give?
Its factsheet sets out an aim, 1.0 bar or more where the supply connects, rather than a promise. We couldn't confirm any refund scheme linked to that figure.
Could a part-closed stop valve be the whole problem?
It can be. Check it turns fully anticlockwise before looking at anything bigger.
Where this comes from
- Your water pressure explained — Scottish Water (archived copy of its page): 1.0 bar, height, pipe sizes, fixes
- Water supply FAQs — Scottish Water (archived copy of its page): trickle after supply work
- Tenements (Scotland) Act 2004, section 3 — legislation.gov.uk: shared pipes
- Shared repairs and maintenance — City of Edinburgh Council: free shared repairs advice
- Lead and your water — Scottish Water (archived copy of its page): homes built before 1970