Plumbing Design for a Residential Tower in Pune: Water Demand, Tanks, Downtakes and Drainage

What the plumbing design decides

The plumbing design of a residential tower is more than the pipes in the toilets. It sets the size of the underground tanks and the pump room in the basement, the tanks on every terrace, the shafts for the downtakes and drains, the sunk slabs under every toilet and kitchen, and the sewage plant and its treated-water lines. Like the electrical load, those spaces must be on the architect's plans and in the structure before the slabs are cast.

Step 1: the water demand

The demand starts from the population - on our housing projects, five people to a flat - multiplied by a rate in litres per person per day. On the Ravet tower, 192 flats at five people each is 960 people; at 135 litres each, that is 129.6 kL a day. On the three Mantra towers, 2,375 people need 304.8 kL a day, of which 94.6 kL is treated water for flushing - almost a third of the demand that never has to be drawn from the municipal supply.

The rate is then split by use, because drinking water, domestic water and flushing water are often stored and piped separately:

Step 2: storage, split by use

The demand is held in separate underground and terrace tanks for each kind of water, so drinking water never mixes with flushing water, and the fire water is never used for anything else. Two examples:

Tank details that matter on site

On the Mantra towers, water is pumped up in two periods a day of three hours each, so the terrace tanks are sized for a full day; each tank has a 2.5 m water depth, 0.3 m of free board, a 600 x 900 mm manhole and an air gap on the inlet.

On the Ravet tower, every pipe through the underground tank walls - the corporation, tanker, borewell and treatment-plant inlets, the overflows, the test drain and the pump suctions - has its sleeve size, flange type and level on a 17-sleeve chart, so nothing has to be cut through a water-retaining wall later.

Step 3: getting water to every floor at the right pressure

Water usually goes up to the terrace tanks and comes down to the flats through vertical downtakes. In a tall tower, gravity alone gives the low floors far too much pressure and the top floors too little. On the Mantra towers, which reach 30 floors, booster pumps feed six downtakes, and pressure-reducing valves bring the pressure down from 3.9 bar to 1.5 bar, so no flat gets more pressure than its fittings are rated for and the 30th floor gets the same pressure as the second. The branches are 20, 25 and 32 mm and the mains 40 to 65 mm, with isolation valves, strainers and meters on each downtake.

On commercial buildings the downtakes are sized floor by floor from the fixture units of each floor - on the Chinchwad office building, with the upper floors on a separate booster zone.

Step 4: drainage inside the building

Each toilet, kitchen and balcony drains into vertical stacks in the shafts. The typical sizes on our projects are 110 mm soil pipes, 75 mm waste pipes and 40 mm basin pipes, with 50 mm vent pipes, 110 mm balcony drains and 150 mm terrace rain-water pipes on the Taloja school. The toilets sit on sunk slabs of 150 to 300 mm - on the Ravet tower, with multi-floor traps, ledge walls and wall-hung closets with dual-flush valves - so the floor traps and pipes fit without a step at the door.

Where the drains of the floors above have to cross a basement or a stilt floor to reach the external lines, a diversion layout at that ceiling sets the falls. On the Taloja school, the basement clear height was raised from 3.0 m to 3.2 m so the diversion could fall properly.

Step 5: sewage treatment and reuse

Larger housing projects treat their own sewage and send the treated water back to the flushing tanks and the gardens. That is why the flushing water is stored and piped separately from the start.

Below ground: basements, storm water and rain

Deep basements collect seepage and rain from the ramps. On the Ravet tower, five sumps with duty and standby pumps lift the water to the ground floor, a sub-soil drain of 110 and 160 mm perforated pipes wrapped in geo-fabric relieves the water behind the retaining walls, and 300 mm storm-water gutters with perforated gratings run at a 1:150 slope. Rainwater from the roofs and the site is led to recharge pits - 12 on the Mantra project.

What to send

To design the plumbing for your building, we need:

• The area statement, with the number and type of flats, shops and offices
• The architectural plans and sections, and the typical toilet and kitchen layouts
• The water source: municipal connection, borewell or tankers
• Whether treated water will be reused for flushing, and the sewage plant location if it is already planned
• The site plan with the municipal drainage and storm-water connection points

Our plumbing work

We design the plumbing and drainage as part of the full MEPF design for housing, offices, schools, hospitals and factories across Pune and Pimpri-Chinchwad, together with the electrical load, the fire fighting system and the environmental clearance data. See MEP consultants in Pune, or send your drawings for a free project review.