SUMP:
After filtration, the pure filtered water is stored in the sump tank. Underground sump tanks are preferred to over-ground storage. Sump tanks generally have large capacity, besides not utilizing usable space. Moreover sump tanks have very little possibility for penetration of light, since the sump lid is mostly situated in a covered place. Further sump with today’s set up of automatic water level controller which also has indicator to know the approximate water level in the sump, necessity for frequent opening of the sump tank lid is greatly minimized.
It is better to have the sump tank lid as tight as possible not only to avoid possible entry of light (which can lead to algae formation and also support living organisms which would certainly contaminate pure water), it would also greatly minimize the entry of crawling insects. As an additional safeguard, one may cover the lid with an opaque synthetic sheet, which would, in addition to eliminating possibility of light entering, also further minimize chances of entry of crawling insects.
Desirable sump capacity:
Many house owners, especially those who want to store rainwater, are confused about the desirable capacity of sump to be built and the number of sumps/partitions. There are multiple sources of water available like tap water (also referred to as Cauvery water in Bengaluru), bore well water / tanker water besides rainwater. There are also queries as to which of these waters can be mixed without compromising on the quality and also what could be the sump capacity desirable for rain water.
Rainwater, if collected with reasonable diligence, would be highly pure than any other source of water. Hence mixing of water from any other source may only reduce the quality of rainwater and not vice versa. Generally water from bore wells/tanker tends to have high to very high TDS (total dissolved solids), while TDS of rainwater is generally negligible. TDS of tap water mostly lies within this range.
For a rooftop area of 1,000 sq. ft. with an annual rainfall in the range of 100 cms., (generally Bengaluru has rainfall around this range), the rainwater annual yield would be around 1 lakh liters. Since it rains heavily during monsoon and sometimes during pre-monsoon, if one has a large storage, most of this rainwater could be stored and put to domestic use.
Storage for rainwater also depends upon the water usage which in turn depends on the number of persons residing in the building. With economical usage of water, per person per day usage may be taken to be roughly 125 liters (sometimes it is taken as 100 liters also, this is slowly being brought down to 80 liters as potable water is getting scarce). Thus if there are 5 persons residing and taking the daily per-capita water usage at 120 liters, the daily requirement may be approximated to 600 liters. Generally there may be a maximum of 100 days between two rains, which works out to 60,000 liters. Since the cost of creating storage of this capacity would work out very substantial, besides issues regarding structural stability of the building, and due to possible availability of other sources of water, one may plan for a suitable capacity.
Also considering the size of the roof (catchment area), for a 1000 sq.ft. roof, a capacity of about 25,000 liters may be planned and for bigger areas suitably more.
It is always preferable to have this capacity partitioned into 2 or 3. One of these partitions may be used for tap water and the remaining for rainwater and in its absence for bore well or tanker water. It would be preferable to have the sumps linked to allow overflow of rainwater into others. Thus when rainwater is in abundance, one may not utilize other source/s.
Even after filtration using fine mesh (as in the case of Effective RWH Filter), there would be some amount of very fine sediment, which would settle down in the rainwater receiving tank partition. Overflow from this tank/partition to other tank/partition would be clear water. Thus inter-connection of tanks / partitions would not only help in storage of the desired source of water but also to the maximum available storage.
Picture of crystal clear rainwater stored in the adjacent sump partition (overflow from the rainwater inlet sump):
- Clear water stored in sump.jpg (167.82 KiB) Viewed 29978 times