Introduction:

In this project we are not going to involve greywater harvesting even if sometimes are more recommended in buildings with small roof area. These systems comparing to rainwater systems are more complex and more prone to reliability problems.

A typical rainwater harvesting system consists of a collection surface, some sort of filter and the storage tank. A separate pipe network can be used to supply the rainwater.

Rainwater can be used safely for irrigation, toilet flushing and washing machines; where the quality of the water used has lower standards. Treating rainwater to a high standard is not usually recommended.

For hotels in urban environments, it is recommended that rainwater is used in conjunction with the public water; as the specific roof surface per head is low. It is essential that the size and efficiency of the catchment area is carefully assessed. If there is insufficient rainwater to supply 100 per cent of water demand (which is likely), then the mains water can be used as a back up to meet either the entire demand or a specific calculated demand.

Is it for my hotel?(See our tool to realise if it is feasible)

1. Calculate the volume of rainfall taking into account the below parameters and see whether rainwater harvesting can meet your demands.

• The average annual rainfall(mm): rainfall amounts vary from region to region
• Collection surface area (m2): the roof or any other surface which can be used for catchment.
• Runoff coefficient: it accounts for the losses of water based on the material of the roof. A good impermeable roof such as corrugated iron will deliver to the guttering system almost all of the water that lands on it.Ground catchments tend to have a lower runoff coefficient as rainwater infiltrates into the ground and flows away as groundwater. Runoff quality also varies by catchment type.

Table 1: Characteristics of roof types

• Daily demands and annual demands (m3):  it is important to realise how much of the rainwater you can be used and where it is more feasible by specifying the demand.

2. Work out the potential water and cost savings.

Economic assessment must be carried out separately for each site: Total installation cost* : 1.Collection tank, 2.Distribution network, 3.Treatment - filters, 4. Power supply-pumping (for example when it is collected on the roof the gravity can feed the water to the point of use) and the annual cost of maintenance, lifetime and replacement cost. Savings will be reflected in the capital cost of water and sewage. The use of electricity is a significant part of operational costs for pumping and UV disinfection. If the rainwater is going to be used for drinking and bathing, UV and chemical disinfection are necessary and will increase operating costs.

Classification: Rainwater harvesting systems can be classified by the amount of ‘water security’ or ’reliability’. These are:

• Occasional: the water is collected occasionally using a small storage capacity tank that can supply the water needs for a short period of time (one or two days). The operability of the system will depend on the season, having different performance in wet and dry seasons. During the wet season the system will be able to satisfy if not all, a big percentage of the user needs, while during dry season alternative water sources will have to be used due to the poor performance of the system. These systems are ideally suited for climates with uniform or bimodal rainfall pattern with very few dry days and for areas that can have easy access to alternative water sources.
• Intermittent: refers to periods when the gross water collection can be divided in two:
  High collection period: long rainy seasons that will meet most or the entire user needs. A small or medium size storage tank is to be used in order to guarantee the supply during days with no rain. Low collection period: long rainy seasons can be followed by dry seasons with almost no rain at all. During these periods in order to satisfy the user needs, an alternative water source will have to be used. 
• Partial: this type of pattern provides for partial coverage of the water requirements of the user, during the whole of the year. This could be achieved either in an area with a uniform rainfall pattern and with a small to medium storage capacity or in an area with a single (or two short) wet season(s) and a larger storage capacity to cover the needs during the dry season.
• Full: With this type of system the total water demand of the user is met for the whole of the year by rainwater only. This is sometimes the only option available in areas where other sources are unavailable. Sufficient a/ rainfall, b/ collection area, c/ storage capacity is required to meet the needs of the user and a careful feasibility study must be carried out before hand to ensure that conditions are suitable.

Gutters: The two main criteria for guttering are to catch the water from the roof and to transport it to the tank. On the surface this seems simple enough, however the relative complexity of achieving this simple aim often confounds, resulting either in poor designs that fail to deliver water to the tank or overly conservative designs with a high cost.

Tanks: Collection tank sizing needs careful evaluation. As the rain usually isn’t falling when it is needed, some form of storage is required. The size of the storage combined with the water demand and rainfall are responsible for the reliability of the system.

*Incentive Grant (ROC): A hotel business would be able to claim the allowance, which it should claim in the return that relates to the period of its investment. If it can't claim all the allowance in the first year, then it can carry the residue forward, but can only claim the normal 20% writing down allowance on the residue.