Overview

SDS rainwater harvesting systems are providing water security for 20 business premises on the Isles of Scilly by addressing a shortage of mains-supplied drinking-quality water.

Brief

The brief from the Council of the Isles of Scilly was to facilitate the supply of rainwater for purposes where potable water is not required.

Background

The Isles of Scilly, situated 28 nautical miles south west of Land's End, Cornwall, comprise approximately 200 low-lying granite islands and rocks, with a population of roughly 2,200, the majority of whom live on the island of St Mary’s.

The islands are one of the most vulnerable areas of the less developed area of the UK to the impacts of climate change, including drought and water shortages. Due to their remote location, they have no connection to the UK mainland water supply systems. The islands rely upon the supply of desalinated seawater for their drinking-quality water; the desalination plant can produce only a limited amount of water and involves a high-cost, energy-intensive process.

The potable water supply must also cope with large fluctuations in demand; during the summer the population increases by up to four times and the islands are exposed to extreme water stress.

The Council of the Isles of Scilly has an important role as a focus for the islands' communities. It is at the centre of the islands’ sustainable development and works closely with partners to achieve this.

The Council received £250,000 of funding from the European Regional Development Fund with the specific aim of helping businesses on the islands install rainwater harvesting systems. Sole trader businesses on the islands were invited to apply for grants, which also required a contribution from the owners.

Objective

To replace as much of businesses’ non-potable water consumption as possible with recycled rainwater.

Requirement

To provide a full-service solution comprising the design, detailed specification, consenting, manufacture / sourcing and supply, transportation and installation of rainwater harvesting and storage systems.

As the successful tenderer, SDS was required to work with businesses to define the modifications needed to their internal plumbing to enable them to use harvested and stored rainwater indoors.

Rainwater harvesting and storage tanks

SDS was required to visit each business premises and advise on the location of the proposed site, layout and size of the rainwater harvesting tank to be installed.

Each tank is connected to as many downspouts as feasible at the property. An overflow ensures that rainwater in excess of the tanks’ capacity will be directed to existing stormwater disposal systems.

Although the rainwater harvested by the installed systems is for non-potable use only, a filter on the tank inlet removes any solid matter including vegetation, soil and other materials from the rainwater entering the tank, thereby keeping the water as physically clean as possible. A rodent barrier fitted to the overflow outlet prevents rodents, typically rats, from entering the tank.

Result

Ten rainwater harvesting systems, with a combined capacity of almost 250,000 litres, were installed on St Mary’s, with the remainder spread across four of the off-islands of St Agnes, Bryher, Tresco and St Martin’s. Due to the constrained space in which to site the tanks, the majority of these were installed above-ground.

Issues overcome

SDS was required to undertake all roles and responsibilities of the Principal Contractor as defined under CDM regulations, in this case satisfying the restrictions of working on a small, island environment. This included arranging travel and accommodation for staff along with mainland and inter-island freight transport for the hardware and tools, as well as obtaining consents and permits such as consent to install, permits to dig / service clearance, and crane permits / lifting plans where required.

Compliance

All water fittings were required to comply with the Water Supply (Water Fittings) Regulations 1999, the Building Regulations 2010 Part G (as amended) and Part H, British Standard BS EN 16941-1:2018 Rainwater Harvesting Systems Code of Practice. All work complies with relevant guidance, regulations and legislation in force.

Fire service access

The reticulated water network on the islands is limited in extent so, when the Fire and Rescue Service is attending fires in non-reticulated areas, it must rely on surface bodies of water, residents’ water tanks and its own water tanks.

Consequently, as many as possible of the tanks are fitted with BS336 female instantaneous outlet valves to facilitate connections.