Quantity Surveying for Water Supply & Sanitation Projects: Network Design to Metering

**Why accurate quantity surveying matters for water and sanitation projects**

When governments and developers build new water supply and sewer networks, budgets can quickly spiral. Pipelines stretch for kilometres, cross varied terrain and require pumps, tanks and valves. Even minor measurement errors can lead to huge cost overruns. A structured approach to quantity surveying ensures materials, labour and equipment are quantified correctly and billed properly.

**Who this helps**

This guide is for quantity surveyors, estimators and civil engineers tasked with preparing bills of quantities (BOQ) and cost plans for municipal water supply and sanitation schemes. It also helps junior engineers understand how to measure and document the works for payment, whether in India or the Gulf.

## Foundations: Understanding water supply and sanitation systems

Water supply projects consist of source abstraction works (wells, intakes), rising mains to treatment plants, storage reservoirs, gravity or pumped distribution networks and service connections with meters. Sanitation projects carry wastewater through sewers, manholes and pumping stations to treatment plants, then discharge treated effluent.

Key elements include:

- **Pipelines**: ductile iron, HDPE, uPVC or steel pipes of varying diameters.

- **Appurtenances**: valves, bends, tees, hydrants, air release valves.

- **Manholes & chambers**: concrete or brick structures allowing access for inspection.

- **Storage & treatment structures**: overhead tanks, ground reservoirs, clarifiers and digester tanks.

- **Pumping & lift stations**: pumps, motors, screens and housing buildings.

- **House connections & meters**: pipes, fittings and water meters.

## Step‑by‑step quantity take‑off

1. **Study design drawings and specifications**: review alignment plans, longitudinal sections and cross sections. Note pipe diameters, materials and class.

2. **Measure pipeline lengths**: trace the centreline of each pipeline on plans; add vertical pipe lengths at connections, allow for pipe lengths into manholes. Include extra length for bends, tees and spigots.

3. **Count manholes and chambers**: refer to the manhole schedule; note dimensions, depth ranges and types (inspection chamber, sewer manhole, valve chamber).

4. **Calculate reservoir and tank volumes**: use volume = length × width × height. Quantify concrete, reinforcement, masonry and waterproofing.

5. **Quantify pumping stations and plants**: measure structural works for wet wells, screens and machine rooms. Include mechanical items like pumps, motors, valves and control panels, usually measured as number of sets.

6. **List valves and fittings**: create separate BOQ items for sluice valves, scour valves, non‑return valves, air valves, bends, reducers and tees.

7. **Allow for excavation, bedding and backfilling**: compute trench excavation volume = trench width × depth × length; include selected granular bedding and imported backfill if specified.

8. **Miscellaneous items**: connections to existing mains, thrust blocks, marker posts, road reinstatement and commissioning tests.

### Example BOQ snapshot

| Item | Unit | Qty | Rate (INR) | Amount (INR) |

| --- | --- | --- | --- | --- |

| 200 mm dia DI pipeline including excavation, bedding, laying, jointing and backfilling | metre | 1,200 | 1,100 | 1,320,000 |

| Sewer manhole 1.5 m dia up to 3 m deep including benching and cover | each | 45 | 26,000 | 1,170,000 |

| 500 KL overhead tank – RCC works, formwork and reinforcement | lump sum | 1 | 3,500,000 | 3,500,000 |

| 100 mm sluice valve with chamber | each | 12 | 18,000 | 216,000 |

| Hydrostatic pressure testing of pipelines | metre | 1,200 | 50 | 60,000 |

## Key formulas (plain text)

- **Pipeline volume** = π × (diameter)^2 ÷ 4 × length.

- **Trench excavation** = trench width × depth × pipeline length.

- **Pump power (kW)** = (flow rate × head × 9.81) ÷ (pump efficiency × 1000).

- **Storage capacity** = plan area × water depth.

- **Reinforcement weight** = bar length × unit weight per metre.

## India vs GCC considerations

In India, CPHEEO manuals and IS codes govern design and measurement; common pipe materials include ductile iron and uPVC. Excavation is often manual in congested urban areas. In Gulf countries (Saudi Arabia, UAE, Oman, Qatar, Bahrain, Kuwait), HDPE and GRP pipelines are prevalent due to corrosion resistance; trenchless methods such as microtunnelling are used to cross highways. Hot climates require deeper burial for temperature stability. Contract terms emphasise testing and commissioning; variation orders are scrutinised, so accurate measurement is essential.

## Common mistakes and how to fix them

- **Ignoring fittings and specials**: failing to list bends, tees and reducers leads to cost shortfalls. Always extract all appurtenances from the manufacturer’s drawings and include separate BOQ items.

- **Incorrect excavation volumes**: assuming a fixed trench width for all diameters is wrong. Use standard trench widths based on pipe OD plus working space and adjust for shoring.

- **Not accounting for infiltration/inflow** in sewers: underestimating flows results in undersized pipes. Cross‑check design flows and include infiltration allowances.

- **Overlooking testing costs**: pressure tests, chlorination and CCTV inspection require time and resources. Include them as separate items.

- **Ambiguous descriptions**: unclear item descriptions cause disputes. Provide clear descriptions with material class, joint type and inclusions.

## QC & QA checklist

- Verify pipe certificates and material approvals before delivery.

- Inspect pipe dimensions, wall thickness and coatings.

- Ensure correct bedding material and compaction.

- Confirm line and level with theodolite/laser at regular intervals.

- Check jointing technique (rubber ring insertion, torque bolts).

- Conduct hydrostatic pressure tests and leakage tests to specification.

- Inspect construction of manholes and chambers – shape, benching and step irons.

- Verify installation of valves and fittings at designed locations.

- Ensure proper backfilling and surface reinstatement.

- Document test results, inspections and as‑built drawings.

## Frequently asked questions

**How do you measure a pipeline with frequent bends?**

Measure along the centreline including all bends. Where fittings are measured separately, deduct the socket length from pipe lengths to avoid duplication.

**What if the actual trench depth is deeper due to poor ground?**

Record the additional depth through site measurement sheets and apply unit rates for extra excavation and backfill as per contract clauses.

**Are pump and mechanical items measured by quantity or lump sum?**

Pumps, motors and control panels are usually measured by number of sets. Installation, testing and commissioning are included in the same item unless specified separately.

**Do manholes count include cover slabs?**

Yes, manhole items generally include precast or cast in situ covers and frames. If separate, provide an item for supply of covers and frames.

**How do you manage variations when the route changes?**

Prepare a revised measurement based on the new alignment, seek approval from the engineer and adjust the BOQ quantities through a variation order.

## Level up your skills

Ready to master water supply and sanitation estimation? Level up with ** – Quantity Surveying & Estimation Level  1** (link to course page). You can also explore BHADANIS**Construction Project Planning & Management Level  5** and **Tendering & Construction Contracts Management Level  3 & 4** to broaden your skills in planning and contract administration.