Monday, 15 March 2021
Calculate the tank capacity you require
Choose the right water tank when harvesting rain water from your roof by calculating the capacity you require
There are a few points to consider when choosing a water tank, not only the colour or the shape but also for peace-of-mind the quality and size.
While you can never have too much water stored, you can certainly have not enough especially to last through a dry season.
To calculate the capacity you require or the size and or number of tanks follow through the simple questions and calculation below.
1. What will be my daily water consumption? (Check the household guide below)
2. How long is the dry period with little rain for the area I live in?
So, for a four person home with a 50 day dry period means they need to have stored at least 32,500 litres of fresh water to last them through when there is no substantial rain to replenish their tanks. This means that with an adequate buffer the owner should be installing at least 2x 25,000 litre water tanks.
If you are required to store water for fire purposes this will also need to be added.
To calculate the amount of rain water your roof can collect, the formula is – 1mm of rain falling onto 1 sq. metre gives you 1 litre of rain water.
After finding the amount of storage you require you will need to choose the right tank. Not all polyethylene tanks are the same but can be differentiated by design and manufacturing processes used for example a tank with vertical parting lines will split open easily.
Ensure the tank complies with New Zealand Potable (Drinking) Water and Food Contact Standards, is fully UV stabilised and has a suitable manhole entry and ventilated lid.
Wall thickness is important, especially in the base side wall area which must withstand the greatest weight pressure of anywhere on the tank and the best manufacturing process is what is termed as a one-piece construction which means the lid or dome is not added on separately.
If your water tank needs to be situated on a hillside or lowered into the ground due to height restriction and/or for aesthetic reasons choose a corrugated style tank that remains fully warranted when buried and especially so with no unsafe cavities left around the tank.
When you are required to install a Fire Service Outlet Coupling Kit ensure the tank wall is strong enough and also that the tank warranty will not be made void with a larger penetration made into the wall.
Some manufacturers offer up to 14 different colours, smooth wall and corrugated wall styles all made from polyethylene which allows you to select the best colour to suit your surroundings and surprisingly the visual variation of the corrugation design really helps your water tank to fit into natural surroundings.