Water and Plumbing Fixtures

Hold one idea above all others: supply and drainage are separate systems that must never meet except across the tiny air gap above a fixture. Supply is water under pressure, arriving clean. Drainage is used water leaving by gravity, carrying soap, hair, and waste. The first runs in small pipes (15 mm to 25 mm) that can climb walls and turn corners freely because pressure pushes the water along. The second runs in fat pipes (75 mm to 110 mm) that can only ever go downhill, because nothing pushes it — it falls.

This is why a tap can sit anywhere you like, but a WC pan or a floor drain is fixed the moment the slab is poured: its outlet has to line up with a drain that already falls toward the stack. When you move a basin 300 mm along a wall, the supply follows easily. When you try to move a WC 300 mm away from its stack, you are now fighting gravity, and that is a structural conversation, not a finishing one.

In most Indian homes, municipal water is unreliable in both timing and pressure, so we store it. A sump (underground or ground-level) collects whatever the corporation gives, a pump lifts it to an overhead tank on the roof, and from there water flows down to every tap by gravity alone. The pressure you feel at the tap comes from head — the vertical drop from the tank's water level to the fixture. Roughly every 1 metre of height gives you about 0.1 kg/cm² of pressure. A tank 3 metres above a ground-floor shower gives a gentle, usable flow; a tank only 300 mm above a top-floor shower gives a sad dribble.

This is the single most common pressure complaint in Indian flats: the top floor's bathroom sits almost level with the tank, so it has almost no head. Designers fix it with a pressure pump on that branch, or by raising the tank on a taller stool. Know the tank height before you promise anyone a rain shower on the top floor — that big drencher head needs real head behind it or it simply weeps.

Trace the clean water from the tank and you get a tree. A vertical riser drops the water down through the building. Off it, branches run horizontally to each bathroom and the kitchen. Off each branch, short legs feed individual fixtures. The rule that separates an amateur layout from a professional one is simple: every fixture deserves its own accessible shut-off valve (an isolation or angle valve), and every branch deserves one too.

Why obsess over valves? Because plumbing fails, and when it does you want to stop the water to one tap — not run to the roof and drain the whole house while the family waits a day for water to refill. A leaking basin tap with its own angle valve is a five-minute fix; the same tap with no valve means shutting the main, draining the line, and a flooded floor. Insist on a valve under every basin and WC, a valve where each bathroom branch leaves the riser, and at least one drain point at the lowest part of every line so it can be emptied for repairs.

Drainage has one job: keep moving downhill so solids and water never separate. That needs a steady slope. For a 110 mm soil pipe a fall of about 1:40 (one unit down for every forty along) works; gentler 1:60 to 1:100 suits larger or longer runs. Too flat and the water outruns the solids, leaving them behind to block. Counter-intuitively, too steep is also bad — the water races away and abandons the solids just the same. A back-fall, where a pipe accidentally tilts the wrong way, is the worst of all: it pools, stagnates, and stinks.

Under every fixture sits the quiet hero of the whole system — the trap, a U or P shaped bend that holds a permanent plug of water called the water seal (around 50 mm deep). That little curve of trapped water is the only thing between your nose and the sewer. Foul gases from the drain push up the pipe and stop dead at the seal. This is why a floor drain in a guest bathroom you never use eventually smells: the seal evaporates, the barrier vanishes, and the sewer breathes into the room. Pour a mug of water down a forgotten drain monthly and the smell never comes. Traps also need venting — a pipe open to outside air higher up the stack — so that a big flush elsewhere doesn't suck the seal out like a straw.

Here is the move that quietly saves money, leaks, and noise: put all the wet fixtures on one wet wall. Cluster the WC, basin, and shower against a single thickened plumbing wall, and where you have multiple floors, stack the bathrooms (and the kitchen) one above another so a single set of risers and stacks serves them all. Short pipe runs mean fewer joints, and every joint you remove is a leak you will never have. It also keeps the noisy, smelly drainage on one side and frees the rest of the room.

With the layout settled, size the demand. A standard tap can run 8–10 litres/min; an aerated low-flow tap mixes air in and gives the same satisfying jet at 4–6 litres/min. A single-flush WC dumps 10–12 litres every time; a dual-flush cistern offers 6 litres for solids and 3 litres for liquids, saving thousands of litres a month. A bucket bath uses 15–20 litres; a shower can quietly run 60+ litres if you linger. Multiply by a family and the numbers get real fast — try the Water Budget Calculator on this page: pick your taps, your WC, bucket versus shower, and your family size, and watch the household's daily litres add up so you can choose fixtures that fit your sump, your tanker bill, and your conscience.